I have to echo the general sentiment expressed by those who responded- without a solid suspension set-up your Mister Two will be a seriously compromised machine. (I speak from experience, tragically

) The MR2 is chiefly a sports car that exudes handling prowess, so before supplementing the powertrain ensure that the foundation (a.k.a the suspension and all its encompassing components) is solid.
As I mentioned earlier, I made the mistake of doing a turbo-swap on my '91 hardtop BEFORE addressing the suspension mods and consequently threw the balance of the car completely off. I would recommend replacing such essential suspension components as the sway bar bushings, ball joints, and steering knuckles if they are worse for the wear (I was able to land a solid deal on a front stabilizer bar mounting bracket for just under $20 at toyotapartszone.com

). Trust me, these may not be as glamorous parts as adding after-market sways but they are integral parts that keep your Mister Two planted and stable during turns and are sadly often times neglected. Only after you ensure that these essential components are in decent kit should you move onto upgrading the tires, sway bars, springs, etc.
Hope that my advice helps!