I joined AFROTC after completing two years of undergrad (5 year degree).
a) Yes and no. The only area that you will need to catch up on is RSS (Relative Standing Score AKA Commanders Ranking). This is your biggest hurdle to overcome. Depending on the size of your detachment, it can be a challenge. Other than that, it does not make you less competitive for a rated slot. The factors for receiving a rated slot are RSS, PFA Scores, GPA, FT Ranking (Field Training Performance), and PCSM. You can have good scores in your PFA, GPA, FT Ranking, and PCSM just by personal preparation. RSS will take some work within the detachment. Overall, joining a year late has little impact on your rated slot chances.
b) Be in frequent contact with your APAS. I would suggest meeting with your APAS during the first 2-3 weeks of the semester and ask for their expectations of you during the semester. Then request a mid-semester eval, and final eval. Your APAS is your connection to the Det Commander (improves RSS). Do well and participate often in your Aerospace Studies class. Participation shows your APAS how you think. Actually prepare for LLAB and volunteer for leadership positions. If you really want to prepare, you can read up on the 2018 FTM (Field Training Manual) and the AFI 36-2203 (Drill Manual). You can start to memorize the Warrior Knowledge that is presented in the FTM. I would suggest going on YouTube and find Det 088 Drill videos, those will help you prepare for drill and give you a nice visual reference.
PM if you want more advice, happy to help.