New User with Various (Some Minor) Problems to Solve

You can clean all transactions using database tools module when you finish practice. Then you will be able to delete those entities.
2.
For what you need i think you should use customer accounts system for customer credit or debit.

And for reservations you can use pre-order tickets

Sorry I don’t have time now to give more details. Try to search forum for more information about customer accounts. Maybe tonight I’ll have some time if you need.