I rode across country in 1977 using a 5 speed freewheel... that wheel is still usable today. I have both cassette and freewheel bikes that get ridden regularly. As long as the components are in good shape and you are maintaining things well I don't see an issue with riding either one. Carry the removal tool if you want, most well equipped LBS should have all the tools in stock, especially if they have been in business any length of time.

Aaron