For the treats during the 4-7 time period, be sure to check the hours of the restaurants as it gets closer. Right now, Liberty Square Market closes at 5pm and is not open during the party (at least per the WDW website and what I've seen reported). Cheshire Cafe was closing at 3pm and reopening at 7pm for earlier parties but now looks like it will be open during the pre-party time. If it stays that way, I would be sure to prioritize the whoopie pie because the only time you will be able to get it is between 4-5pm.
I've also personally found that I get less done during the 4-7pm period than I plan. So I would identify the 1-3 things that are most important for you during that time so that if things take longer than planned, you can change your plans on the fly.