Welcome aboard! Run what you brung until you decide what clubs you want to autocross with. If you want to run SCCA and/or ER, you will have to follow their strict classing rules. If you want to run NTAXS, BMW or Porsche, it's a more wide open,generic classing. You can run all clubs of course, but they have very different classification rules.
Having said that, if the suspension is original on those cars, it's going to be very tired. Typically the first upgrades are tires, bump stops, shocks, front sway bar. Cars must be mechanically sound to pass the mandatory inspection before you run with any autocross club. Basic stuff like..lack of wheel bearing play, fluids, belts, secure battery, etc.