I would like to get an AR-10 carbine; I’ve been shooting a 270 bolt action for 50 years.  I would like light weight, short length, low cost, and capable of accepting components from different manufacturers.  This will be used for target and varmint, maybe hunting depending upon its/my performance.  I have been reading for about 4 weeks and am still left with questions and, I am sure, misconceptions.  Here are some of my questions:
1)Are the uppers and lowers equivalent across manufacturers?  If not, how do I differentiate?  I have read that older lower receivers are longer and being out dated.  But I have need seen a manufacturer’s site that lists the length or whether it is an old or new design.  How can I know?
2)I would  like the hand guard to extend as far forward as possible on the 16” barrel.  Any hand guard I find for the carbine is only 8”.  Yet some pictures seem to suggest there are hand guards much longer.  How do I find a longer hand guard for the 16” barrel?
3)Is it possible to swap out the barrel for a longer one if the need arises?  Is this something that can be done in the field?
4)I am only looking for hard sites but would like the flexibility to add optics later.  What should I look for?
5)I would like a handle.  I understand that some are removable.  Are there any that are readily removable?  Does this have to be coordinated with the hand guard?
6)Is there any options for a short overall length and extendable stock?  I am tall and the ability to lengthen on demand would be great.  I don’t believe I have anything to store in the stock.
7)I would like there to be a sling.
8)What are the considerations flash hide?  I expect to be in low light levels at times and in brush.
9)Any considerations for buffer tube / spring?
10)Any considerations for trigger?

Any additional suggestions are welcome.

1.  No-they are all over the map when it comes to compatibility.

2.  It's very easy to use a rifle length handguard with a 16" barrel, unless you have a Front Sight Base on the barrel.  Most people install a low profile gas block under a free float handguard.  This would be ideal for your application.

3.  Barrels can be changed with relative ease on the AR10, but not in the field, unless you have a complete separate upper, or a quick change barrel system.  Many people have dealt with increased performance by shooting more aerodynamic bullets, as opposed to looking for longer barrels.

4. Almost all the AR10 configurations out there support rear iron sights, as well as optics.  Front sights are another story, but will be fine if you use a 12" handguard with a top rail, and mount your front sight there.  Very few people use iron sights on AR10's, since there are so many affordable optics that are also rugged.

5.  There are detachable sight housings, commonly called the "carrying handle", even though that design originates from the first AR10's, which had a trigger style charge handle in that area.

6.  Yes. You can use most of the AR15 telescoping stocks on the market.

7.  Sling is easy

8.  There are almost endless flash hider combos.

9.  You need to carefully select AR10 appropriate buffer and spring combos, with one of 3 different tube lengths.  

 * AR15 carbine tube/AR10 carbine buffer & spring
 * ArmaLite/Vltor A5 tube/AR15 carbine length buffer (heavier) & AR10 spring
 * AR15 rifle tube/AR10 rifle buffer and spring

10.  There are tons of trigger options.  A good hunting trigger can be found that will fit your likes.

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~MODS

LRRPF52,

Great!  Thank you for all the info.  

BTW, is the picture taken in Utah?