I think I would switch things up. With the Epcot monorail re-opened by then, your less painless option would be doing Epcot during the day and taking the monorail to MK for the Boo Bash. No bothering with busses from the other parks. For that work, just drive to the TTC in the morning and take the Epcot monorail from the TTC to Epcot. When Boo Bash is over, the monorail or a ferry will take you back to the TTC where your car already is.