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Let's see.  First welcome to retroland!  Right now any barrels are gonna be hard to come buy and amount of coins spent will more than likely dictate availability.  I'm guessing you're getting 4 or 5 A-1 upper receivers?  Sight height should be same for A-1 or A-2 rifle or carbine.  Besides barrel diameter only difference in FSB is sight post and forge marks.  Raised FSB F marked was a flat top carbine system agenda.  Wouldn't worry too much about sights as I've never personally had much problem in this area and a longer sight post will cure if problem arises using a flat top receiver which you are not.  .  A-1 round sight post with 5 adjustments and A-2 square post with 4 adjustments without going into too much detail.  Both will get you where you need to be accurately.

Until you decide on which barrel kinda hard to gather the small parts unless you possibly want spares.  

For drilling a barrel for FSB installation the ease would kinda depend on your machining skills and equipment access.  Correct would be with a jig,  approximately $150 if store bought.  It can be done without a jig but if it's off the sights are gonna be off.  Won't usually matter much until one starts shooting a little distance.  Patience is key to retro and parts gathering unless you just want to throw coins at the hobby.  In retroland the authenticity of the build and attention to parts detail is probably one of the main objectives.  With that said build what you want with what is available,  shoot it and have fun.  You can always swap out later if and when it starts to bother you or you find the correct pieces.  Many here swap parts as they gather for correct build.  Sell the old part or build another weapon and install the new part.  Vicious circle in our AR hobby.  Good luck.