the frame is a 2009 Giant TCR Alliance 1, 105 front derailleur, crank shimano SG-X 50F 34F (think it's the stock 105 crank and chain), pedals and seat post clamp stock, and a used saddle. I need a lot of parts including a rear derailleur, cassette, shifters, and brakes what parts can I mismatch within the shimano & sram brands?

also I've been thinking about setting it up as a single speed because it will save a lot of cash and weight. I need brakes (brakes, cables, levers etc), seatpost, headset, stem, handlebars and a fork, (i think I have a wheel or two that are ok)