No, sights will need to be acquired separately.
No this is only an upper. Those would come on a complete lower.
Unfortunately, those are not available. There are videos on youtube of similar kits after assembly has been completed that may be of assistance though.
Yes, this kit will work with any AR15 stripped lower.
There are two barrel lengths available, a 10.5" and a 7.5". They will list the barrel length and handguard length.
The outer diameter of the buffer tube is 1.25". Here's a link to a brace that would be compatible.
https://www.opticsplanet.com/strike-industries-ar-pistol-stabilizer-brace.html
The thread pitch should be 5/8x24. It should be capable of being suppressed.
A complete upper is not an ffl item.
While there are no listed domestic shipping restrictions, if there are any issues shipping to any location you would be notified once the order has been placed.
Yes, the user can remove the flash hider. It is 5/8x24 threaded.