As far as what to charge....who knows?
Like Roger said I have seen college freshman home for the summer charging $20 and former pros charging $100 an hour.
Depends on the area you are in ect.
Somewhere in the middle is probably the sweet spot.
As a dad who has taken my son to several instructors I can give some advice from that perspective.
Be organized. Nothing worse than paying someone and having him seem distracted or have him have to look for a catchers mitt to borrow.
Know what your approach is with technique. Parents will know if you are winging it. This doesn't mean every student gets a cookie cutter approach. But, know what you are looking for. It sounds silly but nothing is worse when a kid a struggling hitting and his coach watches for 5 minutes and says "looks good to me." There is a thin line between cookie cluttering it and just making changes to make changes. Know what your approach is to technique as a teacher.
Know your approach as a teacher. You are teaching children mostly. They will be nervous, uptight and or unsure to varying degrees. Figure out you can best communicate information to kids. Being approachable and friendly goes a long way to breaking down walls. One thing I have seen with kids over and over is they will "yes" when you ask if they understand when they have no idea. Remember, they are kids (even at 15 or 16) and don't want to look foolish. Make sure they understand what you are saying before moving on.
Ask them questions and get them communicating.
Keep it simple. Using fancy medical terminology will only confuse the kids and or parents. Break it down into easy to understand pieces.
Chit chat and story telling is for before or after the lesson.
The one (yes only one) coach I liked that my son went to was friendly chatting with him as they warmed up. As soon as the actual lesson began it was all business. He did not take lapses in concentration as an excuse.
Be honest with parents. You will have parent with MLB dreams show up with a 14 year old who can barely tie his shoes. You don't need to say "he sucks" but you shouldn't feed their delusion either. "Lets worry about getting him on the JV team first. If he decides its fun and wants to keep playing, we can take it from there."
Have fun. If you find yourself getting impatient or pissed off at the kids teaching kids is probably not for you.
As for the opening a facility/travel ball thing I would take some time with that. Work with an existing travel organization. See how much work goes into it, the expenses, what the income level really is.