We haven't actually had the ceremony yet, but we're pretty far into the planning process, so I can tell you what we've found out so far.
For context, we're going on a RCCL cruise in April, and getting married in Nassau with an outside planner.
First, from everyone I've talked to, DO NOT USE THE CRUISE LINE'S WEDDING DEPARTMENT. I have to agree. Just dealing with them for group-non-wedding events, they're a pain in the ass to work with. We went with an outside planner in Nassau who has done bunches of cruise weddings, and it's a much better experience. You also get a lot more bang for your buck, and a lot more control over the details.
We'll see about photography...We're bringing our photographers (who are super awesome and amazing and flexible) on the cruise, and planning that they'll act like "guests with fancy cameras" more than photographers to avoid the outside vendor rule. The cruise ships photo packages were crazy expensive.
For residency requirements, we're avoiding that by having a symbolic ceremony, and then doing the legal paperwork once we get back into the US.
In terms of ceremony vs reception, we're doing ceremony+reception on Nassau for a couple reasons, the main one being NOT WANTING TO WORK WITH THE CRUISE LINE. Also, because some people are flying in, and so we want them to be a part of the fun, and not just the 30 minutes of the ceremony. We're going to be at the venue from 10-3, have lunch, play games, hang on the beach, and then head back to the ship. We're figuring that back on the ship will be the "afterparty", if we're not collapsed from exhaustion by then, lol.
Good luck! Let me know if you want any more advice from one cruise bride to another