um..wow. i think you need to do a lot of research. i will try my best to answer some of your questions.
1) buy your barrel chrome lined or not from the dealer. finding someone that will chrome the barrel aftermarket will be difficult much less the cost of such an undertaking.
2) as long as you have a decent barrel, barrel extension (which comes attached to your barrel), and bolt, you won't have to worry about headspacing.
3) if you want an aftermarket front sight (which is unneccessary) then you will need to install it with set screws (bad) or pay a gunsmith to install it with taper pins (good). i would just recommend you stick with the original FSB.
4) just buy a CMT upper and bolt carrier group
here and pick a barrel
here you won't likely be more accurate than any quality barrel, so just pick one the right length and twist rate for you. dont worry as much about reconfiguring the placement of sights. good luck.