Well heck, if you already have handgun, a rifle is the next logical step.
Getting into barrels twists is another can of worms. Generally speaking, if all you are going to shoot is 62gr and lighter, then the 1:9 will serve you nicely. If you think you might want to shoot the MK262 or heavy TAP ammo, a 1:7 might serve you better. The 1:7 will shoot the lighter stuff. The caveat is that a 1:7 might exaggerate the inconsistencies in cheap ammo. Theoretically a 1:9 twist might shoot crap M193 ammo better than a 1:7 twist simply because the 1:9 twist spins it slower so it doesn't wobble as much while it's flying. Now, if you feed the 1:7 the good stuff, it will shoot it every bit as well as a 1:9 twist.
Of course, I'm just talking in general terms. You could very well get a 1:7 that shoots the cheap lighter stuff every bit as well as a good barrel with a 1:9 twist. On the other hand, you might get a 1:9 twist that will shoot 77gr projectiles very well. My Rock River (or is it a Bushmaster?) 1:9 barrel shoots 77s just fine.
The point is, don't loose too much sleep over the issue. The only thing is that the arguably better barrels, like those from Bravo Company, Noveske, Spike's, Daniel Defense, etc., come with 1:7 twist. If you like one of their rifles, just buy it and don't worry about it.
Personally, for my goto/play rifle, when I need a barrel I just get a name brand. Like I said, I used either a Rock River or Bushmaster on mine. It runs fine.