Firstly, do I need an oil pressure indicator on the dash?
Nope (but it would be wise to have one), you only have to have Speedometer which must be lit up, tell-tale for when indicator are flashing, unless you can see both sides flash when in driving position. Tell-tale to indicate rear fog light is on, tell-tale to tell you brake fluid low, tell-tale you're on full beam & finally if your reverse lights are manually switched you have to have a tell-tale for that.
Secondly, do I need a spare wheel?
Nope
Apologies if these are obvious questions.
Don't apologise, just ask
Alan...