The ATP CTP course is a really spin up trainer for the airlines. They told me have fun because it's the one time where you can't fail anything while you're in a sim. As for renting airplanes, I wouldn't spend a lot of time and lose seniority over trying to fly a Cessna. Maybe a few hours if you wanna get some muscle memory back. Review IFR rules. Right now in the Regional world, the only way to wash out is to have a bad attitude and lack of eagerness to learn. The most difficult thing in training is the single engine ILS I'm not to sure if spending hundreds to thousands of dollars on a baron will help you out that much though.

My biggest recommendation is to go to a regional that has AQP training for initial because that is train to proficiency (you won't fail for being 20 feet off on steep turns).

I say spend too much time and money in before because of the ATP CTP program. It was like going to airline training before going to airline training. Get in, get your currency, get on to a major. Seniority is everything