Galway - Inismor - Doolin

This is a good question so email [email protected] and ask about their cancellation rate due to weather conditions compared to Galway’s Rossaveel port.

The ferry seldom sells out so there's really no need to book more than a day or two in advance. Besides, you'll want to check the most recent weather forecast before committing to a specific date. The vessels are relatively small craft and tend to rock and roll in even the most moderate of sea states ... making for an uncomfortable crossing if you're at all prone to motion sickness.
You're right to be concerned about potential cancellation of service - they'll scrub the daily run in stormy weather or during periods of high sea states.
We've been to Ireland numerous times and in all seasons and my qualitative opinion is that April weather is notoriously unpredictable - can vary from sunny, gorgeous, and the sea as flat as a millpond to "Victory at Sea" if you're unlucky. Bottom line is that I probably wouldn't risk the ferry to Doolin if I had a hard commitment waiting at the other end - could be a recipe for disappointment.
You might want to consider flying over and back. These guys offer daily service for a reasonable cost. Would add a scenic flight into the mix as well as avoiding the potentially uncomfortable crossing by ferry.

Thanks a bunch.
We typically enjoy being onsite after all the tours leave for the evening, but it is starting to sound complicated for this visit.
Maybe for this visit we will just opt for a tour out of Galway weather permitting
Thanks again !

Actually, I wouldn't give up on Inishmore - it really is a great day out whether you overnight or not. I'd just be cautious about relying on the ferry.
Aer Aran is a great option.

Galway is my least favorite place in Ireland. It’s a good base for Inishmore and Connemara and that’s about it. I believe I would have enjoyed Inishmore more had I spent the night.

You could attempt your plan and if the smaller ferry to Doolin isn't running due to weather, just return to Galway on the big ferry. The Rossaveal ferry will operate in marginal weather that will cancel the Doolin ferry - horrible weather might cancel both, and really horrible winds could cancel the air flights.