I plan on making the ride with a support vehicle and having supply pickup spots pre-planned throughout the route. ... I'll have around 126 days to complete the ride, which doesn't include the days off.A couple of things stood out for me. Why are you planning supply pickup spots if you have a support vehicle (or even if you didn't)? Can't you just buy what you need wherever you are? What sort of supplies are you going to have sent to you?
126 days (not counting days off) to do 4400 miles is a very leisurely pace, probably more than you need even if you are taking it easy and stopping to visit a lot of hospitals.
I suggest you specify exactly what percentage of the sponsorship money will support your trip and what percentage goes to the charity.
Have a great time!