For the record and to avoid confusion, most people call the 601 bus that runs between Huntingdale Station and Monash Clayton the "601" (not run by Monash, needs a valid myki and the rest of it), and the bus that runs directly between Monash Clayton and Caulfield the "shuttle" (which is run by Monash, needs a valid Monash ID). Going from Caulfield station to Monash Clayton, the times are about the same between train+601 (~20 mins) vs shuttle (15-25 mins). Personally I'd go with the train route just because trains are more frequent.
@OP, travel time is pretty shit. I've done 2 hour journeys to some hospitals which mean to get there at 7am I had to wake up around 4.30am, and I got home around 7pm. It's shit, but you learn to cope when you have to. Some people study on trains/trams/buses which saves time later, I personally don't mind a cheeky nap.
Also, I think it's far too early to rule yourself out of undergrad med before the UMAT is even sat. If you approach it with the mindset that you're going to fall short, you'll fall short every time. Have some confidence, work a bit harder, and who knows what could happen. You don't need to be a genius to get into medicine (I'm a good case in point LOL) and you don't need top scores in either the ATAR and the UMAT; you just need to do well enough and back yourself at the right times.