your choice of the 3 replacements, z3, expensive to fix and have no boot, mr2 not bad but try to go for the t top version, personal choice would be the mx5, son has one, an l plate, which you may still be able to get modern classic insurance on, and as for nothing to do to them, they still need fettling, early ones with the pop up headlights i prefer the look of, and go for an 1800 not 1600.
they are a little cramped but hold the road well and are a fun drive, watch for sticking break calipers on them, and upgrades..... plenty of add on bits depending on the depth of your wallet/purse, but get the moss catalogue for a fairly comprehensive spares list, including a supercharger.....
and at the end of the day keep dropping in, be nice to hear what you end up with...

the project at birth, watch it evolve...I hope...