The Deep Bay marina is a pretty good one - are you certain there's space there still? That's a great part of the Island to live.
Getting to Desolation from there is more sheltered - going up Baynes inside Denman and then out over the Comox bar - generally in summer you have relatively calm conditions.
Getting down to the Gulf Islands, however, may be less comfortable. Check any summer day with a decent NW wind and you'll find that area from Winchelseas to Entrance Island will have the strongest winds. This is a common summertime pattern that can sit for days, so you'll be wanting to wait for the appropriate weather window. In a SE system it really whistles up there and Sisters is usually the high spot. It is close to 50nm from Deep Bay to Dodd narrows, the entrance to the Gulf Islands. That's a long way with a 20 something footer - not a one day jaunt.
Learning to sail in Baynes Channel is sheltered, watch for currents during larger tides - and sandbars.
Anyway - I don't mean to sound discouraging, if you get a good boat all this is doable with patience and some experience, and it's a great place to start. Summertime is Desolation is more about the destinations than actually sailing, so the boat you're on is less of an issue. The next thing to find out is how long can you live without standing headroom down below?
In all likelihood if this goes well for you you'll be looking for ways to upsize before you know it!
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)