The Marketplace bus stop opens at 8 a.m., but direct service is limited to a few nearby resorts and the Epcot resorts. Getting to more distant resorts, such as AKL & the MK resorts, may take as long as 90 minutes and sometimes a transfer. Transportation cast are stationed at the bus stop to assist you until 11 a.m.
Full service starts at 11 a.m., but also starting at 11 a.m. all buses stop at PI & TL (when open), so you need to build in an extra 20 minutes for that.
Buses run from all resorts back to DTD starting around 8:30 a.m. Buses leaving the resorts between about 9 a.m. and 11:30 a.m. stop at TL on the way in, which adds about 10 minutes travel time.
Yes, Bess can get to the resorts on her own.