Are you staying on property? If so, you will need to take the Extra Magic Hours into consideration. Magic Kingdom opens an hour earlier that morning for resort guests, and we've always found morning EMH to be sparsely attended and a great way to see and do a lot in a short period of time.
Since you only have a few days in Disney, I encourage you to check the
park hours page and see which park is open later (or earlier!) for each day of your visit and plan accordingly. Sometimes an hour or two can make a huge difference!
I will strongly caution you that seeing 4 parks in two days, as well as leaving the parks completely to have dinner at Downtown Disney, is a
highly ambitious plan. We are very seasoned WDW travelers and honestly, I'm not sure that I would attempt such a feat. So very much time would be spent traveling back and forth between resort, parks, and dining locations, that it would be a lot of wasted 'park time' that could be spent in one spot. It's definitely do-able, but it will not be a relaxing trip by any means, and won't give you time to stop and smell the roses - or soak up the pixie dust, as the case may be - and we have always found that pixie dust to be one of the very best parts of a Disney vacation.
Good luck!