How is my Scotland Itenirary?

I think I may shift back my leg and add Aviemore from March 25th to March 27th. Then everything else would be the same, except 1 less day in Inverness more likely since the space between is shorter travel time wise. Is that reasonable?

Hello again Jessie,
Looking broadly OK.
I might be inclined to do 2 nights at Kyle of Lochalsh. Then as well as Eilean Donan (aren't you interested in visiting the Castle, rather than just an external view) you could add in beautiful Plockton (on the train from Kyle).
Inverness- isn't there anything else that interests you there- the Great Glen and Loch Ness (bus to Fort Augustus and later Urquhart Castle, or a boat trip down the Loch to the Castle), maybe the Black Isle, maybe Fort George, even Aviemore/the Cairngorms/Boat of Garten ospreys/Grantown on Spey. The Black Isle doesn't crop up often on this forum, but I think would suit you- a lot of history and nature out there. The bus to Culloden Battlefield doesn't run on a Sunday. You'd need the citybus to Culloden Village and walk up. Fine if it's a dry day but I'd hate to see you have to do that if the weather was bad. So really that's taxi.
All the above other Inverness trips are eminently possible on transit.
If you did 2 nights at the Kyle and the extra nights at Inverness that would seem to me, personally. to be a better use of the extra nights. One day in Inverness just feels a bit cursory. Ireland feels a bit of a dog leg.

Are you looking to see the east coast of the Republic of Ireland (well worth it) or to do Northern Ireland. If the former Dublin would be the better airport to fly to.

From Belfast I'd think about the Giant's Causeway and places like Portrush, on the Antrim coast, although the east side of County Down (out beyond Bangor is perfectly do-able). If it was the start of the trip I'd suggest Rathlin Island but that's far too risky at the end in case the weather closes in.
April 9 fly back to Scotland for your last night to be safe to make your TA flight next day.

Plockton is beautiful and well worth finding.

Eilean Donan looks wonderful from the outside but the interior doesn't live up to the outside. The castle was rebuilt from a ruin at the beginning of the C20th, so isn't as old as it looks... Admire and take a picture and then move on...

Adding an extras night in Inverness would allow you to visit Fort George, built after the Battle of Culloden to control the Highlands and crush any future Jacobite rebellions. It remains one of the largest and most impregnable fortifications in Europe. The word impressive just doesn't begin to describe it.

You could also drive to Dunrobin Castle, family home of the Dukes of Sutherland for over 700 years and built to impress (and subjugate...)

Alternatively if you are wanting another destination for two nights, then think about Oban. To the south is Kilmartin Glen, possibly one of the best areas for prehistoric remains. There are more pictures here. There are details of a walk around the site here.
Alternatively, you could spend a day on Mull and Iona or else visit Seil and Isle of Luing...

As you are not driving you can go to Dunrobin Castle on the train to what was the Duke of Sutherland 's private station. You leave Inverness at 1041, have 2 hours at the Castle, and arrive back at Inverness at 1706 (doesn't run on a Sunday).
It is a request stop, what you call a flag stop. So you ask the conductor to stop on the way up.
On the way back there is a brand new system in place, just installed, so no American visitor and few English either will yet have used it. Instead of putting out your hand to ask the train driver to stop, you press a button on a platform console within 20 minutes of the train being due. Note that this applies to every other request stop on that line. It is so new that it is not confirmed yet whether it is fitted to Dunrobin Castle which is not open for the year until 26 March.
This video explains how the system works-
https://www.youtube.com/watch?v=5ghk-OHrG3I
Getting to Kilmartin without a car is not easy are there are long gaps in the bus service numbers 23/423.
https://passenger-line-assets.s3.eu-west-1.amazonaws.com/westcoastmotors/WCMO/23-timetable-20220815-6599817f.pdf
The same is true of bus 418 to Seil and the Isle of Luing, hence why they were not suggested originally.
https://passenger-line-assets.s3.eu-west-1.amazonaws.com/westcoastmotors/WCMO/418-timetable-20220905-b23b9e13.pdf
North Cuan is the ferry port for Luing (there is no longer a bus on the island- it was a postbus and all postbuses have been withdrawn), so quite a bit of walking), Ellenabeich is on Seil and is the port for the tiny island of Easdale.
Note that to get to Fort George you catch bus 11 to Ardersier then about a 20 minute walk (scroll down on this timetable, which also has the Sunday bus 3 to Culloden Village)-
https://tiscon-maps-stagecoachbus.s3.amazonaws.com/Timetables/North%20Scotland/Highlands/Inverness%20Guide%20from%20040722.pdf