When do modifications become 'necessary'? Maybe never... maybe soon after purchase.

There's no substitute for trigger time with your rifle, but the learning curve dramatically improves with getting your hands on differently configured rifles. Strike up a conversation with guys at our club and they'll usually hand ya their firearm if expressing the least bit of interest. You may find that a longer handguard to extend your support hand is what you want. Or that Geissele trigger is the way to go. Or the guy's rifle with an adjustable gas block and muzzle brake that stayed still in your hands shot after shot was so nice to shoot... or or or. Or you may find that you like your rifle just the way it is.

You've made the first step entering the world of ARs... after that there's no telling what direction or destination you'll find yourself.

Enjoy that new rifle.