Clients type their goals and best times. This one is an example we made.
Ben Tran PT puts a short form in the app. Clients write their goal and the times that suit. The enquiry lands on his phone. This one is an example we made.

They quote or invoice from the same app. No web inbox.
You can. A Lead form suits coaching where you need the goal before you name a price. You can switch to a Quote page later.
No. They use the web page. Only the business needs the app.
Get the app. Add your enquiry form. Make your page live and share the link.