Your thought process seems pretty sound. What is your team's strategy? With that speed I don't think you will make the top basket.. and you will have to position yourself within a few feet of the other baskets.
If you still want to use that motor set-up, you could use larger wheels? Or you could look into a gear box with a lower gear reduction. My team is using this
gear box with that
motor. The reduction is 3.67: 1. We are also using 8 inch wheels. Our estimated exit velocity is: 9.5 m/sec (includes a 1/4 speed reduction). That would allow for us to shoot from 15 ft away- for the top basket. If these
motors come back in stock we are going to use them instead and get an exit velocity more about 14.3m/s (also includes 1/4 reduction). We could then potentially sit 30 ft away.
If you haven't already you might want to find a trajectory calculator or run your own equations in Excel.