I can give them one piece of free advice: Start with one aircraft and see how it goes.
OK, two pieces of advice: Don't forget to have a website that is not liable to be hacked, can hold your clients details and money safe and give you control over everything - that means, don't outsource it. Have the people running it sitting in a room where you can reach out and grab them (warmly) by the throat. Also, have the site built ready to interact with your App. You don't have to have that day one but folks will expect it and, again, it will give you more control.