You have a lot of reading to do! The bright side is that it will be time well spent. This is a great community and I think it will allow a well-informed decision as to what car you will buy.
I think you will love the 124 Spider. The best thing to do is visit the nearest dealer and drive one. Learn about the three main versions of the car Classica, Lusso, and Abarth, and review the options you want. Then if the dealer wont get you what you want, simply order if from a dealer that will and have them ship it to you.
Here is a brief overview,
Classica: It's a pretty good deal, and for someone who plans really heavy mods, it may be the best choice since you won't be paying for expensive shocks and wheels you will probably change anyway. It's relatively few features means it's closer to the roots of the original 124. However, the stereo is terrible, it has no nav, no backup camera or a lot of other goodies people like. It does have power windows, A.C. and other creature comforts.
Lusso: Like a classica, but with lots more creature comforts. Think of it as a loaded classica.
Abarth. Like a Lusso, but with an upgrades suspension featuring really great Bilstein shocks, nicer wheels, louder exhaust, limited slip diff, and a sport button which changes some driving dynamics.
I hope that helps. I love the 124, and it seems most people who have driven one feel the same way.