Hey and welcome to the board!
I am no expert by any means but I can cover a couple of your questions.
First.......the AR is way more modular than the AK and there are TONS of upgrades/changes you can do to it. The AK will be less expensive. There will be people chiming in who have strong opinions on which to get but I like both.....but I do like the AR more. But that's my opinion.
As far as the carry handle goes.....that's easy. Get an A3 flattop. That may make no sense to you now but give it a month or so of reading these boards and you'll understand everything.
Also, there are lots of options for optics as well. Too many for me to go into here.
My main point of advice is to read these boards and do your research before buying anything!! A litle time reading here will help you to make a decision you won't regret!!
And once again, welcome!!