Best advice I could possibly give: start by defining, in specific detail, exactly what-all you want the car to do (or not-do, or do differently). In terms of real, practical function, not in terms of how many horsepower you think you want it to have (that number is good for bench-racing, and nothing else).
Be sure to factor in that a car that goes faster also needs to steer and stop better, and these cars mostly don't steer or stop well in stock form, so a good chunk of your money-time-effort budget needs to go for stuff like that. A higher-perf engine also requires more in the way of a cooling system, a sturdier transmission and rear axle, etc. Y'might want to see
here to get some ideas about accounting for non-engine aspects of your build.
