I am looking to get an NAS drive to store all music, photos, DVDs, and other assorted documents in one place under our control, attached to our local network.

Maybe sooner than later there will be CCTV security cameras, etc.

I have been looking at Synology DS920+ system (4 bays) with maybe two 4 TB drives and room to expand. I doubt that we will need much more than that, currently, because right now we have maybe 2 TB of photos and other documents, but we have maybe 100 physical DVD/BluRay disks that we may digitize and ditch the discs.

The review videos have been pretty positive, for the most part. The software that comes with it seems pretty good and the system seems to be easy to install with an ethernet connection and (uninterruptible) power supply. I like the idea of a RAID configuration for redundancy, and maybe having a mutual agreement to back up our data at our daughter's place out of town and vice versa to have off-site backup for both parties.

The only drawback besides price is the 1 GBe cable that comes standard with this system. The complaint seems to be that 10 GBe cable should have come with this as standard, particularly if you want to do photo editing.

The Question: Is the transfer rate an issue if all you want to do is store and stream content, but not edit it on the device? What if multiple users are accessing the NAS simultaneously; is that in issue if you are not doing video editing?

Thanks in advance for any advice.

The DS920 only has  1GbE ports anyway, it can't even do 10Gb. 1Gb is more than adequate for your use case. Even if it did support 10Gb you'd have to upgrade all your other equipment (switch, pc, etc.) to take advantage and 10Gb equipment is still fairly expensive. Link aggregation is another feature it supports which is helpful if you have multiple devices connecting simultaneously.

As said nothing in your home likely supports 10gbit ethernet anyway. If the NAS has the ability to do link aggregation/bonding then that will assist with multiple users accessing it concurrently. A single 1gb ethernet gets you about 120MB/s of data.

It can bond the two ports.

There are some 10g NAS hardware out there and you are right to try and go that direction if you can.  I was looking at a pizza box size server that included two SPF+ interfaces which would allow 10G connection.  However; I went with the more classic solution of a NAS.

Bottle neck are common at the NAS when two or more users hammer the device requesting full bandwidth copies of large files to the machine at the same time.
My NAS I can limit how much resources a single person can access at a time. This prevents one person from hogging 100% of the performance.  
The down side is you won't get best peak performance for when the system is used by one person.  

You can have choke points in your network too esp if more than one computer shares the same line to the NAS.  The NAS does support dual 1G lines so it might be possible to aggregate the connections into support of more than one network.  If I was designing a new setup for home use; I would have a 10G backbone with support to prevent the network from being the limiting factor.  

DS920+ is the newer version of the DS918+ that I have.  Not bad hardware; I did manage to brick the hardware once when upgrading the the software.

Common speed improvements..
 verify that you have max RAM installed in the box;
 go for the dual SSD caching to speed up system performance.  I would recommend 2 @1T devices to provide good levels of caching of the device.
 stripe devices that need pure max speed...mirror drives if they need to be fault tolerant.

Use external HD to backup you device.  In fact; I keep 2 USB dries hooked to the machine for such uses.    File transfers to and from the NAS seem faster when transferring from USB3 directly connected to the device.

If you want to use raid, it is best (but not always required) to use the same hard drives for all members of the raid.

If you only stream from the device as in playing back movies with no problem; you should be able to play (not decode) 2 or 3 devices at the same time without issues.  The transfer speeds playing back at 1080p won't peak load the network or NAS.  If I am running a backup; trying to play a move from the same device is sluggish but once started seems to work fine.    
 
I have run VM off of the device without issue.  

Note:  Some of the special software that you can install in your NAS to support such things as CCTV security cameras, etc. may require additional license fees.

Great; thanks for the advice.

We are not likely to become power users, so linking up more NAS drives is unlikely.

Ok, great. Our upload/download on ethernet is ~92 MB/s both ways (intermediate level FIOS), so this should not be a problem.

I wonder why the reviews even mentioned this issue? Nerds gotta nerd?

Thanks, this is very helpful.

We are not likely to have more than one "power user" on the system at a time.

One advertised advantage of the Synology software is that it is said to support a "hybrid" RAID setup with different sized disk drives.

You can use different size drives - but when doing stripe setup for speed I think you will get best performance with same device types for each member of the raid...and you don't have to use all drives as part of a raid (depending on type of raid you setup).

I think you may be conflating some numbers here. Your fios is probably 92 mbit/mbps or mb/s depending on how someone is abbreviating it. It's the same meaning though.

Your home ethernet is 1 gbit/gbps etc or 1000mbps. If you convert megabit (which is what line speed is typically rated in) to megabyte (which is usually what hard drive speed is measured in) a 1000mbps ethernet link gets you about 120 megabytes per second.

Your fios is likely running about a tenth of that speed. It won't affect how fast your storage is. But I'm using it for comparison purposes.

P rep for an eventual drive fail.
I just had one of my RAID drive go TU.

fortunately its RAID so.....

1GBe is plenty fast for home use.  Even that will be overkill unless everything is connected via wired ethernet.

Unless you are doing some pretty serious media editing...1 GbE ports are fine.

We use Synology's fairly exclusively at the office (I even use one as an iSCSI to store the file system for 12 different active VMs) and while I would absolutely love for my manager to tell me to go grab the 10 Gb SFP+ card for the box an run a DAC between it and my main switch (my VM host has dual 10 GbE NICs but only uses one at the moment). I currently have it configured as an LACP though to the switch and that is more than adequate.

Here are some interesting little numbers though. A 1080p stream needs 7 Mbps or less (depending on H.264 vs H.265) to stream across a network. 4K is simply 4x1080p and requires about 28 Mbps to stream. So you can basically run 35 4K cameras on a single 1 Gbps uplink (assuming your disk read/write speeds can keep up which they should be able to do). So 1 GbE isn't really as much of a limitation as everyone thinks it is. I've actually been designing a new home network for myself and one of the bigger issues in my head was me wanting to support the newer mGig Ethernet standards (such as 2.5 GbE and maybe 5 GbE) but it would really only be needed at the server level. My ISP only supports 250 Mbps and my LANs just doesn't need that much gear to run smoothly. Now I may get to the point where my router is routing 4+ Gbps but I won't practically need it (especially if my wife continues to perform her media editing via 802.11 standards).

OP, it looks like you have already done your research to come up with Synology DS920+.  I, too, have been eyeing this as an upgrade for my current QNAP NAS replacement.  And just like you, I am not a power user.  I use NAS for backup and streaming PLEX.  And my current NAS is more than sufficient for such task.  Since you need one, I say go for it.  But instead of lousy 4TB HDD's, put minimum 6TB or 8TB HDD in it.  And I recommend at least 3 to 4 HDD's for RAID 5 speed and reliability.

Any interest in rolling your own?  I built my own, significantly more powerful NAS a couple months ago for half of what that Synology costs out of used server hardware from eBay.  Check out serverbuilds.net if you are interested.

I have a Grandstream IP doorbell installed at one of the clinics I manage, there is an app called Surveillance Station that supports quite a few IP Cams or ONVIF.

This is a fun route especially if you start out with a barebones linux box on the distro of your choosing (I personally prefer CentOS but with IBM screwing that one up I have not yet applied for RHeL's new program). I started off with a Ubuntu 12.04 box built on a (new) HP N54L microserver almost a decade ago. That same N54L is running Ubuntu 18.04 on the same 16 GB of memory it started with 9 years ago. Few storage upgrades (larger drives, RAID 0 to RAID 5) but otherwise running as it should.