Hi Mossda,
I live close to Nanaimo which is along the path you're looking to travel, feel free to reach out with any questions or if you want to meet up on your journey.
1. I'd look at the BC Marine Trails map for guidance on camping spots
https://www.bcmarinetrails.org/2. Be sure you have an emergency beacon of some sort (EPIRB/InReach), ideally also a handheld VHF radio
3. Be sure you dress for the water temperature, it's easy to get chilly around here when in the water, for any extended journey I wear a drysuit
4. Be sure to check tidal charts, currents can get up to 10 knots in some of the channels so you want to be sure you're passing at the right time in the right direction
For the boat I'd have a look at FB Marketplace, Ebay and Craigslist, those are going to be your best bets around here, I know there are a couple of Tandems for sale in Washington state, perhaps one of them works out for you.