I would not characterize April as high season. It's still "busy" but not high.
There will always be some anchorages that will be full up. That's most times of year. Imho you should plan to be in to your anchorage no later than 4.00 so you can reasonably come up with a plan B if needed. We operate the same as you - we leave relatively early in the morning to be at our lunch stop for a couple of hours and then get to our anchorage for the night with enough time we can enjoy it before it gets dark. Leverick has some jet skies. Rarely see them used and never seen them flogged through the mooring field. Never seen them anywhere else though we never frequent CGB.

I think there are plenty of places in April with peace and quite that can be enjoyed. But of course "crowded" means something different to every person.