Aran Island (Inishmore) overnight stay

When I went to Inishmore I wish I had spent the night but I would have left on the first ferry from Rossaveel and returned the next day on the last ferry. Since you’ll be coming from Dingle, I recommend two nights on Inishmore and skip sleeping in Galway. Inishmore is much more unique than Galway.

First, Rossaveal is the right choice. The B&B we stayed with in Kilronan would not accept reservations from people coming via Doolin due to weather unpredictability. They may have had an uncle that worked on the Rossaveal ferry :-)

Second, we spent a single night there, and the quality time was when the last ferry had left. In June the population swells to awkward numbers and I'm sure it's worse in Jul/Aug. We arrived on the noon ferry, ate lunch at a small cafe and spent the afternoon walking along the bay, almost to the airport, stopping at a few church ruins and one bar for a Guinness. Joe Watty's for dinner and trad music that night. Next morning we rented bicycles and pedaled out to Dún Aonghasa and a few other places including lunch. Pedaled back, bought some sweaters, had a beer at The Bar and got on the 4pm ferry back to Rossaveal. I don't know what we would have done for a second day, as we're not the type to just hang. There isn't that much to do. I'd opt for Galway, as we love the nightlife there (music). Depending on where you're heading, you might consider adding Clifden or Westport instead.

There is another option for getting over to Inishmore: flying doesn't really cost that much more than the ferry. The trip only takes about 10 minutes and would eliminate the possibility that rough sea states could cause the ferry to cancel ... or at least would save yourselves an uncomfortable boat ride across to the island if conditions are choppy.
I imagine that your BnB host would be happy to hold your bags until check-in time while you tour the island.

I recommend staying two nights on Inishmore. I have stayed on the island two times and visited Ireland five times.

Inishmore is custom-made for bicycling. I rented a bicycle at the port and had it most of the day because it was such a great ride.

The island has wonderful antiquities worth visiting. The Dun Aengus stone fort is the most famous, but there are others worth seeing.

It also has a museum covering the history of the Aran Islands.

And it is magical to walk on Inishmore during the day as well as at night. The stars are beautiful to look at, and the island is serene.

I understand that there is a place to watch Irish dancing and hear music, though I did not do that in part because I last visited Inishmore in 1999.

I have never been to Inisheer island, but a friend told me she took a ferry to it to see the Synge Chair and house the writer and playwright had stayed at in the early 1900s.

On one of my visits, I hired a man to take me on his pony and cart. I would avoid that. Bicycling is better. And I even took a guided tour with other visitors. I would skip that, too. The museum is better.

We stayed in the glamping cabins which are quite convenient to the port/ferry dock. We rented e-bikes. Unless you are in fabulous biking shape, I encourage you to rent the ebike version. There is something almost magical of riding up to the top of hills without wondering if you can possibly make it.......

Renting a bike for all or part of a day to explore the island is a good suggestion. My only advice is that if you're considering doing so that you invest in a good pair of padded cycling shorts. You can thank me later.

Joe Watty's often has music. I bicycled the length of the island in 2019, there weren't e-bikes, I was 69 with multiple back surgeries and a knee transplant, wearing jeans, without ever having to stand up and pedal any hills.

We were on Inisheer in '97 and my most vivid memory is that every house was enclosed by a stone wall, upon which was sitting a border collie. The houses are fairly close together, as the grazing fields are "out of town", hence the dogs. We walked around a large portion of the island between ferries, although I'd rent a bike if I did it today.