Newbie Question

hoppers should all fit any gun. Bog standard gravity hoppers are cheap as chips but it could be a plan to loook into mechanical hoppers if you will be modding the 98 to give faster rates of fire or even if your just shooting nice and fast. You may have noticed the need to shake the hopper in order to feed the paint properly and avoid breaking paint. If you invest now you'll always have it and a good one will go with the guns as your kit progresses. Im sure theres a good second hand market for them. That being said a cheap gravity hopper will probably do.

Tanks should all be the right fit. The size of the threads on the regs do vary (i know a guy that had about 50 smart parts bottles sitting in a lock up since they sent the US sizes and then went out of business). As long as the tank was designed for paintball and you know what size of thread you need which only varies in large geographical shifts like US have one thread and all of europe have another you should be fine.

Using air v Co2 is another discussion that im sure is covered elsewhere.

I don't know good places in the states so i think you just need to shop around. Bear in mind that the casual secondhand market for A5's is always pretty good. So local forums would be your best bet