Great advice by all above. You are being resourceful with regards to earning some money to help cover costs and seeking out advice from a site like this. Use that same resourcefulness to find great instruction and mentoring within a reasonable cost. This time of year, there are lots of college players home for the summer that will be willing to work with you with mechanics of throwing and hitting, advice on conditioning programs, long toss programs, etc. Much of your goals to throw harder and hit harder will come with your physical maturation but your full potential can only be reached if you are doing things correctly with regards to mechanics. You may find that resource in other places as well. Maybe one of your HS coaches is well qualified and willing to help you over the summer with extra time.
I strongly second the suggestion to do some research and starting to put together a list of schools across multiple playing levels. You don't yet know what your baseball fit will be and there are far too many things out of your control that can prevent you from matching up to one or two specific schools. So, go ahead and completely go for it with Notre Dame as your first choice but have some really good other choices as part of the plan.