Do you want separate home alarm and camera systems?

Because you can get some of the functions of a home alarm system by setting up an appropriate camera system.

I honestly use my cameras more than my home alarm.

Let me give you a "for instance."

I have multiple cameras on/around my home.  They do several things for me.  They record on a constant basis to a central NVR (Network Video Recorder... also called a DVR), and they also provide real-time alerts independent of that DVR.  They also are accessible from my phone, allowing me to check on things any time I desire.  

So the DVR records... that's its job.  That's what it does.  It does this around-the-clock, and provides a repository of evidence and recordings to sift through if something happens.

But it doesn't provide real-time alerts (some DVRs can, provided they have alarm inputs, but that requires running additional wiring to the DVR from various sensors, which isn't always feasible).  

So I wire sensors directly to my cameras, and configure the cameras to send me alerts based on what they detect.  You can do the same thing with IP cameras and their built-in "motion detection" alert ability, but you're going to quickly discover the limitations of that modality.  VMD (Video Motion Detection) is what the cameras do internally in software, and it's based on changes in the scene detected by whatever algorithms they use.  When the scene changes enough, they trigger "alerts" to do various things (save images off-site, email you, trigger other devices, and so forth).

But VMD sucks...  It generates many false alerts, and eventually you'll stop paying attention to those alerts.  It's the classic "crying wolf" phenomenon.  Clouds, car headlights, birds, windy days, insects... all generate false "motion" alerts.  

Sensor-based alerts are NOT the same.  Quality PIRs (passive infrared motion sensors), reed-switches, induction-loop sensors (to detect passing vehicles), and such are FAR more reliable than VMD.  False alarms are almost unheard of (provided the sensors are placed appropriately), so when a sensor-based alert goes off, you KNOW to pay attention to it.  

That is how I get real-time alerts on what's going on around my home.  If the PIR in my driveway goes off, I KNOW somebody or something is there.  If one of the reed-switch sensors on my garage-door goes off, I KNOW that door is being opened.   I have a dedicated email account that ONLY receives alerts from my cameras, and that account has specific alerts on my phone.  I use an email relay service to send/receive those emails (costs me a few buck/year, but saves me having to run a server on-site).  They arrive on my phone seconds after those sensors have tripped... and those alerts come complete with images of the event... so I now have off-site storage of those images, in addition to local storage.  

This all may seem like too much, and you may not want to go through all that hassle... but it's DIY-able.

So an indoor, static scene is perhaps the only exception to the no-VMD rule.  That might work OK for you.

In terms of door entry, Mobotix has a pre-built kit for that.  It consists of a video doorstation (180-degree panoramic camera, 5-6MP), an RFID-card reader, cards, an indoor remote display screen, and an electric door-opener module.  

It's not cheap, but Mobotix stuff never is.  The good news is that their stuff is extremely high-quality, and offers a gazillion options within the software.  There's really nothing else like it on the market.

Link to kit

Depends entirely on the number of cameras, and what software.  Most of the major software manufacturers give you a calculator on their website to determine what specs you may need.  

Just to give you a rough idea, hit this page in the big CCTV thread.  It will give you an idea of PC specs.  

Any decent quad-core processor should work.  Enough memory, big drives, a high-quality PCI-E network card (like Intel Pro/1000 or similar), and you're pretty much set.  Don't waste money on a video card... integrated video will be fine.

ETA:  do NOT use the motherboard-integrated ethernet port.  Add a high-quality network card.  The difference between a good Intel server-grade NIC and some MB-integrated NIC is significant.

For basic coverage and VMD for alerts, the Reolink should work fine.  You don't have to get too fancy with that part of it.

The wiring is the hard part... particularly in a two-story, or a home without an accessible attic.  

An experienced low-voltage guy might not be a bad idea... they will often charge by the drop, depending on difficulty.