You have to know the differences between the turbo and supercharger which seems nobody in here knows very much about turbo's.
I personally would go for turbo. Superchargers are instant, but you cant tune them very much. It seems you need to do alot of research on the workings of both units before you even consider buying. If I were you, I would go with a moderate sized turbo, nothing big becuase I hate lag. Then get a big ass fmic. All the piping, bov, all the lines you need, and all the other parts. Get a nice boost gauge and turbo timer. Without any internals you wont be able to push much boost, maybe 10psi safely. Maybe more idk Im not familiar with miata's other than swapping in big ass V-8's and also the mkIII turboII engine.