Eden Rock is 500' from the cruise port and it's a mess downtown when the ships are in daily. I don't know if it would be a good place to find a buddy in the afternoon since many cruise divers do morning dives there then go eat/shop before tendering back out to their ships. Esp. ones with early departures. By 4PM it was deserted - we had to find the mgr. to rent us tanks - he was in back cleaning up. Asked us to be back by 5 so he could close.
A better choice might be Sunset House, it's 5 mins. south of town and is the de-facto dive resort on Cayman. My Bar there is full of divers and all afternoon we saw small groups shore diving there.
Or go the other way (NW Point) and try Divetech at Cobalt Coast Resort - the other dive AI. There's going to be divers there. Lighthouse Pt. is their other location but it's a small condo complex so less likely.
Turtle Reef could be another option but one afternoon we were the only divers. If you did want to pay a guide, Sundivers is on site there and Ollin works with Happy Fish Divers to provide guides - even at night.
There's three places to get tanks on Cayman outside of the on-site dive operators at the above^. None of the above (except ER) allow tank removal from the premises. Eden Rock,
Divers Supply in West Bay and the dive store on the south end of SMB. Can't remember the name but it's in the strip mall just south of Treasure Island Resort.
IMO Cemetery Reef is a better snorkel. It is on the north end of SMB though. All the other SMB dive sites are too far off the beach to swim to although you'll see dive boats out there daily.