I have been to Vancouver Island several times and explored it from Port Hardy to Victoria. It is beautiful like a small version of Canada with every type of landscape you can find in Pacific Canada. In summer it is quite busy especially in the better known tourist destinations. You will find any type of camping from full hook up RV Parks to remote Rec Sites or wilderness camping only accessible by high clearance vehicles when it is dry or 4x4 when it is wet. If you go to Tofino and the Pacific Rim NP or around Victoria you won´t be alone. If you explore the Forestry service Roads between Port Renfrew and Bamfield on the West Coast or the North around Port Hardy, Coal Harbour, San Josef Bay it won´t be busy. The islands between Vancouver Island and the Mainland are nice too. In August we take the ferry from Bella Coola to Port Hardy and then explore Quadra Island and Cortes Island before heading over to Lund and Desolation Sound.I can't answer your question, but wanted to mention we did an Orcas Island trip in our previous pop-up camper. Ours was our first pickup/camper ferry trip which was neat. It was a rainy Sept. trip and mopping up 1/4" of standing water (condensation; not a leak) from under our mattress was what instigated the sale of that brand camper and purchase of our CAMP-X. We planned to take the CAMP-X to Vancouver Island but then the borders closed.
Would expect crowds in the summer but no first hand knowledge so your trip report will help us plan for next year. Ha.
Just the stuff you've likely already done: Check Ferry schedule as they had some things out of whack/closures last time I checked. And the boarder-crossing requirements are still changing now and then so be prepared to adapt.
When arriving in Victoria get the Backroad Mapbook https://www.backroadmapbooks.com/ . These Mapbooks are the bible for anyone exploring the Canadian backcountry.
Have fun Stefan