There are a few guides around for removal of the body of the MX5 from its powerplant and frame. They all miss a few bits out. I did mine a couple of months ago and its fairly straightforward. Keep all the nuts and bolts and plastic fasteners, you can use lots of them later, label everything you can - I haven't put the loom back together yet but I am sure all those labels will help no end. In fact label anything and everything.
Taking the body off was fine but I did everything on my own and actually dragging the body on the hoist was a bit of a struggle but its fairly straightforward.
Keep the fuel tank and fuel filter - the filter bracket will save you having to make one - the tank will save you having to make the screw in fittings for the pump and level indicator.
If in doubt - keep it - if not sell it. I've made about £150 profit on selling the bits I didn't need and have a free engine, gearbox, prop, electrics and instruments, can't be bad.