I noticed that there are a number of unused connections on the top right of the board and one of these is labelled +5V. Does that come from the power supply?
Yes.
However, we don’t really recommend to use them for other purposes, except when a very low current is drawn, to avoid excessive dissipation in the regulator.
I was thinking of adding a small fan to the front, with heatsinks on the chips.
Better use a 12V fan and run it from the power supply, maybe put a small resistor in series to drop a couple of volts.