You don't know how many hotels Mears will be stopping at between Rosen and MCO.
BAGS services the Rosen Plaze. You can check your bags, and get your BP, at your hotel. I think the charge is $10-$15 per passenger, in addition to your airline charges.
JMO but the 12:40 is probably cutting it close, even without checking luggage. Check Rosen's website. They deal with a second shuttle company.
A frequent flyer, on another internet board, said a person who never missed a flight is a person who has wasted too much time in airports.