Hello Mtsai!
This is an interesting problem, and I'm sure you can appreciate that the problem is related to what climb you are approaching. Parking Lot Wall at Smoke Bluffs - you can probably get away with flip flops. Phyllis' Engine - probably hiking boots, maybe even mountaineering boots with glacier travel equipment. But, I'm sure what you are looking for is a more generic response. I like to share my own experiences with learning how to rock climb and getting better, so here are my thoughts.
1. I wear approach shoes - La Sportiva Evos, at the moment. Anything with a bit of ankle support and good tread means you won't be fighting with the approach and draining your energy before you get to climb. This is probably as good as you will get for most rock climb approaches (and descents) that exceed 10 minutes, without having to haul heavy boots up a climb. As for slipping and sliding on the trail (which I read in your question) - a lot of that goes away with practice and time. Learning to move on unstable terrain doesn't come quickly, unfortunately. I was raised scrambling in the Rockies, where you learn to move in shin deep scree. Lots of patience required! Bottom line, don't get stressed out over the rest of your group. Find someone who moves at your pace, or is willing to dial it back to stick with you. That, or don't worry so much about being last, so long as you eventually get to the start of the climb.
2. Technical skill - seek out partners and groups that are better than you, and learn in the field. People love to share their knowledge. That said - very important - be absolutely transparent in your skill level. No one likes someone with an over inflated view of their ability, and losing trust of potential climbing buddies is a death blow. It can take a bit of time to find people - club trips to crags or climbing gyms is a super place to start. Its all about networking and meeting people.
3. Courses - I hope I don't get blackballed on this, but the ACC Vancouver is doing a great job with specific niche rock climbing courses. The ship might have sailed with signing up, but I think it's worthwhile taking a look. It's also a great venue for meeting other people who are similarly learning that particular skill. We have our mentorship program, which is a fantastic way to get involved with a defined group of likeminded climbers and a knowledgable mentor. You'll have to wait until next year for that.
Good luck!
Shannon