You just type in the location you are at like Aston Waikiki Sand Villa and to where in Uber you would like to go like saying Hanauma bay in the where to and an ap will come up with how much it will cost to where you are from like Aston Waikiki Sand Villa hotel to Hanauma bay within the Uber app. Hanauma bay also has a shuttle to and from Hanauma Bay which has a reservation on their website. Hanauma bay has a website with all FAQ's frequently asked questions section and verbatim on the Hanauma bay website.

Yes the entrance takes both Master card and Visa. The snack bar also takes Master card and Visa. If you Google Hanauma bay a website that says Hanauma bay state park has a section with frequently asked questions. On the FAQ section they have a shuttle reservation for 25$ American dollars per person. I would suggest the shuttle as parking can be trouble. The price for Hanauma bay entry is 7.50$ American dollars.

Yes you can, at least one snorkelling/diving rental place in the main street in Waikiki rents fins only.

Buongiorno Gianluca, dopo le 09.30/10.00 la baia si riempie di persone ed è peraltro difficile posteggiare. C'è da dire però che verso l'ora di pranzo con il sole più alto, l'acqua è più trasparente. Buon viaggio

Most tours only stop for about 5mins so you can view bay from the top.

I think there were a few shaded areas.