To answer the "profile" question, I guess I made some assumptions (any of which may be incorrect).
Usually, information captured for forms like this is stored locally on the user's machine in the form of a "cookie" (of course, it could also be stored on a server, as well). Cookies (or server accounts) are often indexed/referenced by the user's login account on the machine.
Some (not many, but some) drivers have multiple cars and/or run in different classes in different events (AX vs. DE vs. TT, or even X cars).
If the profile information were indexed (or authenticated) by the user's login, then there is no easy way for the user to have multiple car profiles. If the profile is stored on the server, then the user must authenticate to the server by some means (other than local login) to select the profile.
Thus, IMHO the simplest way to provide multiple profiles is to explicitly allow each account to have more than one profile and to be able to select from a stored profile.
Re: PayPal - after hearing the comments on the MC/Visa payments, it may well be worth investigating PayPal linkage. Many very small companies doing far less than a few thousand a month (70 drivers * $40 = $2800) have found PayPal worth it for the elimination of credit card billing issues.