You've chosen a good route. The shortest route would be across the Mission Bridge, through the village of Matsqui, turning right onto Harris Rd. (Inter-Provincial Hwy.) (56 ave.), crossing over the freeway to re-join 56 on the south side and continuing west through Langley and onto highway 10, crossing over the freeway onto Ladner Trunk, following it west to highway 17, taking highway 17 to the Ferry. This route has more steep grades (between Matsqui and East Langley) then your route. The most dangerous section of your route is between Mission and Whonnock. Most of it can be by-passed by using the parallel road between Mission and SIlverdale just north of the main hwy.
As you've updated by using Silverdale Road, the only other section of concern is between Ruskin and the start of the 4 lane Lougheed hwy in Whonnock which is only 3+ kms. long.
The 56 ave route through rural country until Langley has light traffic but you're riding in sections that are shady, hilly, and windy with little shoulder.
The last time I used the Ferry system while touring I just "rolled on" without any concern about if it's being full. Once on they'll either direct you to where to park your bike, or just go to the front and fasten your bike against the side rails out of the way. I've used the Ferry system from Tsawwassen, Horseshoe Bay, Port Hardy, Prince Rupert, and Haida Gwaii without any problems, but I do keep my valuables in a light pack with me when I leave my bike down on the car deck. Hope you and your friends have an enjoyable journey.
Rodriguez Shiftless street fixie with S&S couplers, Kuwahara tandem, Trek carbon, Dolan track
Ferry: at the end of Hwy 17, you will get on a causeway that takes you to the actual ferry terminal. As you approach, you will see the ticket booths, with electronic signs for the various destinations. You can pretty well ignore these, as you can buy tickets to any destination from any ticket booth. The actual bike ticket booth is on the extreme left of the booths, so you'll have to work your way across the traffic to get there (don't worry, the traffic is slowing down by this point). The actual bike ticket booth is usually closed, though, so you just roll up to the adjoing booth in the car lane. It will usually say "Gulf Islands," but heed my note above.
To get to Victoria, you want to go to "Swartz Bay." Or just tell them Victoria, they'll know. You then ride right to the berth (they'll give you the number at the ticket booth). There is a waiting area for bikes there. The ferry usually arrives at just after 35 minutes past the hour, offloads, then loads the bikes first. They'll give you two tickets. Have the one with the "code word of the day" in your hand as you walk across the ramp, you'll need to give it to the dude on the ramp. Once past the ramp, you can get back on the bike and ride to the other end of the ferry, where you'll see a bike rack, or if it's full, you can just lean your bike against the side. Sometimes they have rope to tie your bike, but the ferry doesn't sway that much that your bike will tip over.
Usually, you'll get one of the older "Queen of" class ferries for the Tsawwassen-Swartz Bay route. These are single-ended ferries, which means that they load at Swartz backed-in, but they arrive in Tsawwassen bow-forward. This means that when you load, you are at the stern of the boat, where the galley is located. So the Pacific Buffet is right above you! The ferry then does a 180 coming out of the dock, then does another 180 when it gets to Swartz Bay. If you get a newer German-built "Celebration" class ferry, it's double-ended, so all bets are off.
Also, last time I took a ferry, they had free wi-fi at the terminal and on the ferries. If you're not going to the buffet, they also have a regular cafeteria and a snack bar. If you're going to dine in the cafeteria, get there as fast as you can. The lines get really long once the car passengers get on. But you've got a good head start!