You don't need colour codes, connect live & neutral to the lower terminals, either way round, and I'd also connect the earth wire to one of the screws, the bottom LH one seems to have a tag there already.
Again if the output is AC you connect those terminals to the AC connections on your rectifier, either way round, it doesn't matter.
For the full 50 amps you'd be looking at 6mm^2 cable.
I have some old jump leads that I could utilise but they are only 4mm, too small?.
Cheers