Wow, where to begin with this...

First you need to establish your goal for the car. Is it going to be a weekend toy, built for autocross/road racing, Street drags etc. Are you looking for 300,400 or 500+hp

What is the current overall condition of the car as it sits now. Are there any things on it you are looking to change in the immediate future, or are you ready to just save up and play later? Mechanical issues now may cause your budget to go into the red pretty quick with a rotary. You need to know if the motor has ever been overhauled, and who and when it was done. You need to know what parts were changed when it was done as well.

You also need to know what the driving style of the previous owner was like. Did they do 10,000 miles a 1/4 mile at a time, or was this driven daily with some spirited driving once in a while on the highway.

Once you answer these questions it will be easier to give you a recipe of what you need to do to meet your goals.