it will be an allen bolt dude, off the top of my head i couldnt tell you the size.
the oil should be clear if in good condition and smell like cats p1ss, at worst dark in colour, if its at all milky then the seals are gone as water has got in. metal shavings will sink so unless you drain it you wont know
and i dont think theyll let you do that
drive it, go through all the gears in hi range and then do the same in lo range - dont forget to reverse too. make sure the change between ratio's is smooth. test all the electrics too
as for bodywork pay the most attention to the front scuttle, rear door corners, inner sills, and the tailgate areas and also the front bulkhead under the bonnet
nothing is cheap to fix, so be careful not matter the model or year