It is possible to take the bus, but it will not be a pleasant experience, the bus from Vancouver is about 12 hours. Greyhound do take bikes, but they charge an extra $50.
I would consider starting in Castlegar and riding the C&W trail to Midway. On weekdays, the C&W is really nice and there are lots of camp spots. The trail is better maintained than the KVR proper and the scenery is beautiful. Depending on your pace, it will add from 1 to 5 days to your ride. On weekends, the C&W has lots of quads and though most riders are careful and kind, it still means pulling over every 5 minutes or so.
Bears are real and you may not see them, but you will see their scat. I carry an Ursack bear-proof bag to keep them out of my food. With the family, we hung our food bag 20 or so feet off the ground. There are many squirrels and coyotes that will also try to get at your food - not so dangerous, but they can make a mess.
I think there is a train back from Hope to Vancouver, and there is airplane service from Vancouver to Castlegar.
I did a writeup of our first trip on the KVR and there is a link to it on coldbike.wordpress.com
The logistics change, depending on how fast you ride, on my own, I can put in 100-200km days. With the family, we usually aim for 30km per day. Real groceries are available in Castlegar, Grand Forks, Penticton, other towns may have stores, but the trail actually bypasses many of the towns on the route.
Trail detours are consistently not marked, so having a map is a good idea.
Be sure to have wide tires on your bike. Many sections of the trail are very loose sand and gravel. If you want to get a hold of me, you can do it through my blog.