^ That's a gorgeous car. Guessing you tracked it?
If you can find an NSX in decent shape for a decent price I'd say go for that - it's a design that (to me) has aged just as well as the FD. Elise's make for fun toys though
Have you considered the FR-S/BRZ? It's been getting solid reviews from most people, and at this point in time it's probably a better bet then restoring an AE86, as venerable as that car is. Are you dead set on RWD?
The LS1 VS 13B is like 1HBH VS 2HBH - there's no clear-cut winner online. A safe assumption seems to be that the LS1 gives you more power off the line but the rotary allows for more precision in cornering, though individual opinions seem to vary.