The bus stops at CSR are #1 - El Centro, #2 Casitas, #3 Ranchos and #4 Cabanas. When going to and from the parks, the buses stop at #2 first, then #3, #4, then finally #1, which is the El Centro stop. For Downtown Disney, the order is 1,2, 3 and 4.
The El Centro stop can get very crowded, particularly in the morning during busy weeks. We stayed in cabana 9A in May a couple of years ago and usually got on the bus at the El Centro stop. We never had to stand, but it is certainly possible if you are trying to make rope drop along with many others.
The only time we have ever stood on a bus for CSR is leaving MK after Wishes.
If there is a convention during your stay, the buses will be less crowded as some guests will be going to the convention center instead of the parks during the day.