If he has joint legal custody he is equally responsible to make medical decisions for the child. That would include being told of doctor visits.
The issue of child support could be answered by running the calculator on the main site and using the guidelines set by the state.
The issue of medical expenses is normally agreed upon by the parents and split with them each paying half of unisured medical costs such as co-pays, deductibles, and medicines. If there is no agreement and he is carrying the child on his medical coverage, then the bills probably come to him. He should pay these and then send a copy of the bill to the ex with a certified letter asking to be reimbursed for half of the cost. If the ex is getting the bills, then they should be paid and she has the right to ask for reimbursement also.
If they are not working together or willing to work together then joint custody is going to cause issues. If he is carrying the child on medical insurance, then IMHO, he should be informed of when the child goes to the doctor. He should be informed anyway because that is his child and that information should be given whether or not he pays child support or even gets to see the child…