Buildinga a streaming PC

[streamLT]

I want to build a streaming computer. To which components should I pay more attention?

What GPU to shoose (more or less expensive)? How much does it have impact in video quality?

What CPU to shoose?

I want to put BM capture card with 2 x SDI inputs and sometimes stream to 2 servers simultaneous (with FMLE).

And is it possible to have graphics (and output them to switcher) at same PC which makes streams (inputs video back from switcher with graphics)? Could it handle all these tasks?