We just returned from a long-weekend stay at GF.
Monorail to and from MK - no issues and we used it all times of the day. We were pretty lucky in the respect that we almost always walked right into a waiting train. The one time things were pretty backed up was our MVMCP night - we went to leave the Grand around 4:15 and the line was backed up into resort - had to wait for a2nd monorail (which came just 5 minutes later).
I think GF could do a better job of letting guests know that if they do not have a bag to check they can go straight to the metal detector- it would move people much more efficiently through security.
Monorail to Epcot - it would be nicer if you didn't need to transfer, but it was fine. On the flip side leaving Epcot at the end of the night and the long monorail line and knowing you still have a transfer in front of you - ugh. It took us almost an hour to get back to GF that night between the mass of people and door problems with one of the trains.
Bus to HS on EMH morning - easy - did not share with Poly. We took the bus to FW for brunch after, so I can’t comment on return trip to GF.
Bus to and from AK - no problem, short wait - shared with Poly around 4 pm. Took bus to WL on the way back to see Christmas decorations and have a cocktail at Territory Lounge (Disney ruined this place - changed the drink menu less than 2 weeks ago - it is now filled with tropical vacation drinks - took away every single bourbon or whiskey based cocktail)
We found our favorite way of moving Between the GF and MK - monorail to and boat back. That put us with only one stop each way. We took the monorail back from MK once and the boat was much more convenient (we did not have a stroller or
scooter)
All in all we found all of the modes of transportation to/from the Grand to be great. We only drove to and from Disney Springs - so, I can’t comment on that bus ride.
As for sharing - it has been our experience (here and at other resorts that share buses) that the bus is dedicated to the resort at ropedrop (peak time). Someone please correct me if I’m wrong.