All the advice you have been given about boats, busses and monorails is correct. However, I would strongly suggest you just take a cab. We went from the Poly to the WL to visit family, took the monorail and then the boat, and it seemed like it took FOREVER. It was probably just a little less than an hour (we had just missed the boat to the WL), but it was waaaaaay too long for our taste. For our return trip, we just walked out the front door and spent about $7 and 4 minutes in a cab and we were back. I might be a tiny bit off on the cost or the time, as it was 2 years ago, but not much.
I guess it depends on how much extra time you have in getting to your breakfast. Somehow when we're at WDW, we never have enough time. I now pretty much always cab it if I'm going from resort to resort.
As others have said, though, just plan to take the bus to MGM from WL. No problems there.
Have a great trip!
Leslie