Beware, MK busses are notoriously slow on half marathon mornings. I read yesterday (during half marathon that takes same route as the Feb race) about people being stuck in traffic for 45 min or more. My guess is even Lyft would have the same issue. So I’d either allow plenty of time... add at least an hour to your transport time... or I’d switch to another day or dinner. If you do leave early and it was quick and easy, you can cheer the runners a bit before breakfast as they enter MK!
For the Princess Half Marathon (assuming the same course route is used this year as last year) buses from all resorts go to the TTC - NOT the MK bus plaza - until runners are cleared of that section of the course (I was in MK last year when the last runners went by on Main Street, which was about 8:30am).
So depending on your timing, your bus from POR to MK will likely go to the TTC. If so, take the resort monorail around to CR.
A word of advice, build in plenty of extra time that morning. It all depends on your timing and what's going on between points A and B, but it can be slow going getting around certain parts of WDW that morning.