I meant to rely to this thread last night but got distracted. It's so much fun building a capsule collection but it gets addicting and before you know it, your capsule collection turns from 4-5 essential bags to a a whole bunch of fun bags!!!
Your collections sounds divine!! I think you should skip the 3rd Kelly, seeing that you already have 2 and add a tote of some type - either a GP, a Birkin or a double sens. Totes always come in handy and can fit a laptop in a pinch.
I would also add a clutch though personally, I tend not to use them. Perhaps consider getting a Kelly wallet that can double as a wallet and a clutch and add that 3rd Kelly to your collection.
Here's how it would look:
Casual Throw Around Day Bag - Lindy 34 and 30 (check)
Tote - Double Sens, Birkin or Garden Party
Dressier Day Bag - 32 Kelly (check)
Casual cross body - ball de golf (can this be worn cross body?) (check)
Clutch/Wallet - Kelly wallet
Evening Bag - Kelly 28 (check)
I would also throw in a Bolide just because I love them