I think that you have too many stops in such a short amount of time. You are only going to have a few hours in some of these cities by the time you take into account travel time. These are probably the reasons for the lower level of feasibility that the trip planner is showing you. I would decide which cities are most important to you and cut the amount of cities almost in half. Or if you could extend your trip, that would be good too. Hope it all works out for you!!