If your internet conneciton is flakey, then this is a concern as
flight instructors and desk staff will be using this system
frequently. If you can't improve the connection, then this system is
probably not for you.

That's probably the biggest concern.

In my view, a proper design for a system of this sort would be to have
a locally installed computer program to do the scheduling, and then
providing internet access to that data, rather than having the entire
application internet-based.

A true windows program can provide a much better user-interface, would
be faster, and insulated from internet problems. A loss of internet
capability would only be a minor inconvenience.

Thanks for your comments.