No shoes needed but crocs should work just fine. Water shoes are great too. The area you’ll be snorkeling is mostly clear beach with relatively minimal coral. That also means relatively fewer fish to see. Lots of tourists but still nice but I didn’t see anything. We were inspired by the trio to return the following day to adjacent beaches which had more coral and shoes were needed there. TONS of tropical fish in/around the coral areas, which are super sharp so shoes a must.

We walked 5 minutes to a pick up location.

it's late afternoon. It all depends on where you are in the drop-off schedule. We were the last couple to be dropped off, so it was a little later for us.

I’m assuming there is as our guide asked if there were any vegans on our tour

Between 5:00 and 5:30pm.

By Waikiki it's the Aston waikiki hotel. Lots of island shuttles make stops there

Fumi's Shrimp. Good food and good portions. Your guide will pass around a menu a few stops before lunch and then call in all the orders. Once you get there, the food will be ready at the window. You tell them what you ordered and pay in CASH (no credit cards when I went). You also have the option to buy other drinks if you don't want the bottled water provided by the tour company.

Ohana Island Tours has a Grand Island tour that leaves at 8am. A bit later, I hope it helps.