For someone just starting with track driving, I'd advise sticking with BMWCCA and/or PCA. I think they have the best organization and program for getting drivers started. As you progress in the more advanced run groups, then start looking at NASA and SCCA, especially if you want to get into real racing. Both BMWCCA abd PCA have very good club racing programs but you are of course limited to what car make you can run.
If you just want to run on the track and have fun, then organizers like Trackdaze (I ran with them at VIR) and Chin may be good options.
I do strongly encourage starting with either BMWCCA or PCA to get a good education base.
2004 330Ci: Sport Pkg, TiAg, gray leather, UUC Swaybars, H&R Springs, Blistein shocks, UUC SSK, Autobaun miles (Euro.delivery)