What is the paintball gun called? that will help us with what kind of maintenance you need.
Zap generally makes average paint that is good for just messin around with, it will be fine for your needs.
The shell is fine, the only paint i have encountered first hand that has had an overly hard shell has been brass eagle blue streak
Paintballs are environmentally freindly. It should say so on the paint box as well, the shell will degrade over a few months. Your dads soil will not get messed up.
Shooting the barrel clean is fine, your barrel is fine. If a ball breaks in the barrel you may want to run a squeegee through it.
As far as habing a feed tube instead of a hopper, i would say that depends on the marker you have. As of now i advise keeping the hopper. To stop the jams you can buy an electronic hopper, i suggest an empire reloader or a VL revolution, neither should be more than 50 dollars.
If you havent seen it yet, the sticky i am about to link you to has tons of good information for new players such as yourself.