While the Gulf Islands are a wonderful place to visit, there are some cautions for novice cyclists.
There are almost no level roads on the islands. Hills are frequent, and frequently very steep. Anyone with unconditioned knees hauling camping loads of gear risks knee problems and should be very willing to walk up some hills.
There are almost no paved shoulders. You must be able to get up the hills without weaving, be comfortable with close traffic, and know to get off the pavement when you stop.
Some of the Gulf Islands have developed heavy traffic over the years. After a trip to Pender a few years ago, I won't cycle there again due to the constant "rush-hour" traffic. On Saltspring the main road mostly has shoulders, and the side roads are quiet enough. Galiano is quieter the farther north you go. Saturna should be the quietest since it's the hardest to reach.
Bicycle stores are very uncommon, but with new, but tested, bikes you're unlikely to need them. Generally the residents of the islands are relaxed and don't mind slowing for cyclists. But the weekend cottagers rush around aggressively like they're still in the city.