Considering getting renshuu pro to continue learning Japanese after finishing AP Japanese, but before going to study in college, and maybe even after. So given this background, is renshuu pro worth it for me
Yes, absolutely! At first I only got Renshuu pro because I wanted to give back for all that the free version already offers, but Renshuu pro has even more settings and I am really glad that I got it.
Yes as a pro-user you can get ton of grammar questions and you can also unlock many conjugations for verbs, adjective etc. You might wanna check going to Support renshuu > Renshuu pro.