Do you think it would be smart to cross train into Pararescue... I would sign up for security forces then cross train over?

Absolutely not. I would recommend going straight in for PJ if that is what you want to do. Cross training is never a guarantee. The Prior service program is one of the Air Forces most selective programs. The Air Force’s priority is new enlisted for pipeline slots than maybe back fill with AFR or ANG students and then finally Prior Service.