Hi Denny, welcome to the forum
Siesta? what's one of those? I have a snooze on the plane on the way to Corfu and again on the way back. The last thing I want to do is sleep my Arillas time away. I get up early and go to bed late - I like to think it makes my holiday last longer ha!
As for things to do.. there's something for everyone. I'm a big fan of the day trips. I have done many already in my 3 previous visits and have a few more planned for when I arrive next week
If you wish to stay on the island then I would definitely recommend a trip to Paleokastritsa, San Stef, Horse riding on Avlaki Beach nr Kassiopi, Affionas and over to Agios Geogios beach. If you would like to venture away from the island then there's a trip to Erikoussa & Othoni islands, Albania, Syvota & Blue Lagoon, Parga, Paxos - I have done all of these and would definitely do them all again
I went to Corfu Town as well twice last August, they were both week days though via an organised day trip. I wouldn't recommend Sundays if you're using public transport because I don't think there is any on a Sunday lol but if you're driving yourself there, then I don't see why it wouldn't be a good day to go. Just don't get there too early if you want to shop straight away as many places aren't open properly until after 10am
I hope you have a great time whatever you decide to do