that is try and see if you like it buddy
Ar platforms are all around the most used as it is highly customisable and can switch CQB upper receiver to a long range upper receiver.
as for clothing, go with what you like, games are often based on green vs tan or digital vs analog camo. so go with whatever you like but please no ACU crap ... it is refered as '' I see U''
gear? need good ocular protection don't cheap on that, good boots too. Vest is like you want... chest rig are colder and less bulky but plate carrier often have more space to put shit on if you are like me and like to carry a lot of useless stuff just for the show.
Remember, you need room to fit extra magazines, a good radio and water... nothing more unless you are on a milsim scenario and need to carry more stuff.
basically, you will make your mind by trying it... I changed like 4 times my setup in 4 years. also, don't bring around 14 magazines on your vest... been there done that, useless, bulky and heavy believe me.
cheers and welcome aboard