R9 200 is just a series, with a bunch of GPUs. It's like buying a "2020 Honda Civic," there are a lot of flavors from the base model to the hot hatch version that costs nearly twice as much.
Crossfire/SLI are effectively dead for gaming, so don't try it for this reason (you'd have to buy something used, these have been out of production for a very long time).
As for your other needs, it really depends on what you're using whether a CPU upgrade or a GPU upgrade would be preferable. If this is professional work, a Radeon Pro or a Quadro would be more appropriate than a consumer GPU.