Oban is a nice enough place - been there several times.
Kilchurn Castle is well worth a visit on the way to Oban (free)

Iona is a beautiful place. On a nice day it must be fantastic.
Tobermory is very nice and there are standing stones with easy access on the outskirts of town at the back of the pottery.
I am hoping to visit again next year.

Haven't been to Arran yet - again, hoping to visit next year.
I look forward to reading your field notes!

Hope you have a great time.