First of all, the Christmas decorations at WL are awesome form what I have seen. I haven’t been lucky enough to go during that time but the pictures look beautiful.
The transportation is great. We had no problems waiting on any type of transportation. As you have read, some is not direct, that means the bus or boat may stop at another resort before going to a park. That wasn’t a problem and didn’t take more than a few minutes. You can get to MK by either bus or launch, I recommend the launch, the ride is so relaxing. I haven’t taken the bus from WL to MK so I can’t tell you how long it would take, maybe 10 minutes total. The boat ride is about the same, 10 minutes if you don’t have to stop at FW first.
Disney will tell you the bus or boat will come every 15-20 minutes, that’s right on if not a little long. We only waited longer once in 8 days, I think that’s pretty good.