It will be a plus that you're interested I a Regular career and I certainly recommend joining the OTC as a way to dip a toe in the water and gaining leadership experience.
In terms of joining, UOTCs differ but none are too difficult to get into. Usually entry would be at the start of each academic year, so you may have missed it for 2014/15. But speak to your local OTC - they will be able to give you the full picture.
As for learning to drive - you do now have to learn at Sandhurst but I'm not aware of any OTCs that provide/pay for B-licence driving lessons. There may be some opportunities for minibus/C-licence/cross-country training and testing, but you would need a full clean car licence for those to be open to you.