FSBs that are drilled and secured with taper pins are the best most secure. If you want that added security find a smith to chop that down to fit under a hand guard.

What hand guard you go with is all personal preference. Quad rails are great for adding lights lasers, etc. but they usually weight more.

Go to bowers and see what they have on hand to see what fits your hand the best. You have different length free floats as well.

But someone told me first when I started modding my first AR... Become proficient first before you waste your hard earned money, that cannot be more true. Learn to shoot it first without all the fancy shit, then start modding it. I have gone through so many builds and handguards, optics from cheap to aim points, etc.