Ireland Itinerary

Looks pretty good to me. You've apparently already done your homework and mapped out a good looking itinerary.
With two nights in Cong I'm guessing that you already plan to visit Ashford Castle and do the Hawk Walk, but if not consider those during your time there.
Dropping the car back in Galway, right?
Others here have suggested taking a late afternoon/early evening ferry from Doolin. Apparently there are terrific views of the cliffs from the water when the sun is in the west.
If you're interested in Irish history, particularly that of the Great Famine, consider a slight detour on your way to Westport to visit the Doolough Memorial. The valley itself is beautiful, and the story of what happened there will help put the history of the famine years into rather harsh perspective. Can Google it to see if it might be of interest.
Killary Fjord is quite pretty and there are some nice hikes in the vicinity if you're into that.

Doolin is great for a few nights - we visited in May 2018. FYI the ferry to the Aran Islands won't run if the seas are high. We went to Inisheer and had a great time.

When we made reservations in Kilronan, they refused to take a reservation arriving from Doolin. The ferry from Rossaveal is shorter and uses larger vessels. It's also available as a package from Galway City including the bus and ferry. You could do Doolin/Galway City/Inisheer without affecting the rest of the schedule.

More time in Aran Islands and less time in Cong would be my suggestion.
I do agree that Hawk Walk at Ashford Castle is great. Splurge for the private walk.

For info, others here have suggested flying over to Inishmore versus taking the ferry. Wouldn't have to worry about a possibly rough and uncomfortable crossing on the boat if sea states are high, not to mention the possibility of outright cancellation of service if it gets too stormy. Throw in the fact that you'd be enjoying a scenic flight both ways and it does look like a winner. Cost isn't that much more than the ferry and it's obviously a much quicker way to go. The airport is located about 15 miles west of Galway ... along the same road you'd take to get to the ferry landing at Rossaveel. https://aerarannislands.ie/
Extending an extra day in Clifden would allow you to take the short ferry from Cleggan over to the island of Inishbofin ... one of Ireland's better kept secrets. Some nice shoreline walks over there and it's just a pleasant way to spend a day without the crowds.

The cancellation rates for boat trips (Doolin, Rossaveal, and Skellig Michael as well) seem to be a state secret. I've tried to set up computer tasks to gather statistics, but the websites rarely mention the status. I have a monitor watching the Gill's Bay ferry for an upcoming trip to Scotland, and it's quite easy to gather info.

The owner on Clai-ban Guest House in Kilronan claims that the Doolin boats are "often" cancelled while the Rossaveal Ferry is "rarely" canceled,, although she might have been referring to early June, in particular. She wouldn't take our reservation until we switched (or lied, I suppose).

The proposed trip itinerary is fairly alien to our tastes, so I won't suggest much, When visiting Knowth and Newgrange, you might want to consider the Battle of the Boyne Museum. No amount of reading can clarify Irish history, but this site was enlightening. We also enjoyed the hike and clambering around CarrowKeel, which is in the general area or your travels.

Thank you everyone for your recommendations. Greatly appreciated and my itinerary may be changing a bit.
~Natalie