Is it just me or is that four wires (two whites and two bare coppers) going into the bottom left terminal of that silver-coloured block?

It's the one that has the single copper wire coming out the top (next to the fat black wire)

I thought you were only allowed to connect one wire per terminal screw unless specifically listed?

There's also two black wires connected to the bottom of the left-most 30-amp breaker (in the trio at top left).