That's a big subject! I can tell you that I devoted considerable time and expense to aero study, fee-based consultation, parts fabrication, and on-track testing. I'll summarize by saying it was well worth it because the result let me go through corners faster, and with
much more confidence. PM me if you're interested in further specifics.
You're correct that you've got to balance the front/rear downforce. That's part of tuning the car's overall setup to meet the needs of the driver, so one size will not fit all. Some want a loose car, and some a neutral car; few want a tight car - they're just slow.
The photo below shows our results, and includes the following aero mods:
1) Well-vented hood, with one large pair located just behind & above the coolant radiator;
2) Shrouding so all air entering the front of the car is forced through the radiators;
3) Front & rear tire deflectors (v. hard to see in the photo);
4) Canards/dive planes;
5) Splitter supported by four turnbuckles, and adjustable from 3"-9.5";
6) Motorsports wing adjustable from -2
° to +10
°;
7) Wing uprights made for this car and wing; and,
8) Supporting structure for the wing uprights in the trunk that is welded to the frame rails - the uprights are bolted to the structure and can be moved a few inches longitudinally to adjust wing placement over the rear of the trunk lid.
Note that splitters and wings must be mounted rigidly enough that you can stand multiple people on the splitter, and so that you can use the wing to push the car, both with no deflection whatsoever. You will have a very slight side-to-side deflection of the wing.
