Let's get some facts straight.
C5
Z06 started in '1 model year & ended as '4 model year. There were "FRC" models produced as '99 & '0 model years powered by 350hp LS1 engine. Parts are cheaper, mods are plentiful, and support is massive. If you think Miata has a solid support, wait till you delve into C5 knowledge.
Miata & S2000
You got most info correct.
350Z
It's not as heavy as you thought. It's heavier by a C5Z06 by a few tens of pounds, but lighter than a C5 coupe and 'vert. It's roughly the same weight as my C6Z06. Think of it as a depowered Corvette. Its driving dynamics is lively yet not lively as an M3. It slides beautifully, much better than any of my other cars and yet it has the lowest torque rating among them. Support is okay and mods seem expensive due to the boutique-inclined Japanese brand names.
E36M3
Nice chassis and engine is willing. It's still a favorite of mine for daily driving. The complexity and some of the logic applied to the car left me scratching my head at times. Specimens are quite old by now, so expect the usual maintenance items and a bit beyond. Retrofit and updates are useful at times. No special tool was needed in my 9 years of ownership.