SCCA Autocross is where I got my start in (ahem) 1971 in an Opel GT, then in an Opel Manta, and went on to campaign a Dodge Colt GT for 5 years in the Ohio rally championship series (and rally-cross, which is a blast!) and the MONY (Michigan Ohio New York) series.
Most importantly, I made some of my closest friends through SCCA and similar organizations (IMSA, NARRA, FIA, and of course, our own GFC here) along the way; several with whom I still stay in touch. I've visited friends in England and Scotland, staying in their homes, and have hosted some from the UK, Finland and New Zealand. The bonds you can make are indescribable.
SCCA also has a national solo series, and sanction hill climbs, too; so, you won't get bored.
Best of luck!
FGTB