If you are in MA, you can't use a "Flash Hider" on the group buy lower. It's not allowed by the MA AWB. Get it with a compensator (permanently attached) or better a match grade crown and you will be fine with the top ones.
Twist will have more to do with what you intend to shoot. The heavier the bullet, the more twist you need. 1:8 is generally good for the 62 grain match bullets. 1:7 is for 70+ or SS109 military. 1:9 for lighter plinking rounds. If you don't know what you will be shooting, I'd go with the 1:8 as it will work with just about anything.
Handguards are a personal choice. Nothing wrong with a standard A2 set until you can decide what you need. As with a wood stock, a free floating barrel usually provides the best accuracy. In the AR platform, that means a free floating handguard that only attaches at the rear and otherwise does not touch anything. These have to be rigid, especially if you intend to sling up on them or use a bipod. I have not decided what setup I will use, but a free floating is a desired feature.
As for the last choice you offered, it's a choice you need to make. It's not a bad choice, just be sure it suits your needs. Is that fancy expensive handguard going to be swapped out for something with rails? Can a bipod be attached if that's something you want? Is the sight rail on the gas block a good thing? ie, are you going to mount iron sights? Would a lower profile gas block look better to you?
The Wylde Chamber is a nice feature as it's a little snugger than the NATO chamber, but can still fire NATO ammo.
Your best bet is to decide what you want to use the rifle for and then build it for that purpose. Your best bet for a 'first' is a straight standard A2 style upper (without the flash hider) so you can have something to play with. Then, as you find your preferred shooting, build a custom upper for that purpose.
For me, I have a Colt AR that I'm leaving in the factory A2 configuration and my new lower will be for a scoped precision rifle. But if I had not already played with the 'stock' rifle, I don't know if I'd really know which way to go.
Of course the top feature of an AR is the fact that you can swap out uppers to fit the situation.