I have known and coached many of talented kids who have "had a dream" to go off and do something for themselves that would have truly made them feel positive and happy about themselves. Only to be given advice that made them put that dream on hold and never do it! Tomorrow is not guaranteed to us. You are a young MAN of 18 years you have the world before you and if you feel strongly enough to man up and put your $4000.00 on the table and further educate your self in something that you feel is positive, fun, you are good at and makes you happy GO FOR IT!!
I will be bold enough to say that you will probably be one of the youngest people in your session, and that in it's self should make you wonder why? Why are so many older than I interested in further there knowledge of this admirable profession umpiring?
Waterford Michigan is north of Detroit, so I guess it is safe to say that you ump games April through October. This gives you plenty of time to take a few classes at a local community college if you choose. Umpiring is a physical job, so your education and pursuit of a degree is a great idea.
Live your dream not mine or anyone else's! Be happy.