I've been both model and participant, the first waaay back in the mists as a teenager at an arts high school in Toronto (taking that robe off the first time was the hardest thing I'd done to that point and maybe since) and then I took classes at OCA (later OCAD). Much later, classes at Sheridan College and then when we moved to Cape Breton, I started modelling for a collective in Sydney, when a friend here invited me to alternate weeks with her. We have very different body types and approaches to poses, so it was a welcome change for the artists in the group. On my non-sitting weeks, I'd draw.
In my experience on both sides of the easel, generally in a class that length there are a dozen or so 30 - 60 second gestures for warm-up purposes, then some slightly longer (5 min) poses and then 1-3 longer poses. Often this is discussed among participants and models will also sometimes invite suggestions. I imagine payment will also be made clear.
You're doing well with the conte! I like working with it for life drawing, charcoal too. We used paint in a couple of classes I did, which was fun, but I think you're right to stick with the conte, at least to begin. Most classes/studios have easels, my favourite was the very first class I modelled for; they had donkeys which you could sit on or upend and stand at - like to find a design for that and make one! If you're not sure and want to use an easel, bring yours (I would). I prefer not to use good paper for these sessions and usually stick to cartridge pads, 18x24. Fun to experiment with white, newsprint, toned tan and gray.
I wouldn't worry about being seen as "competition," whatever your ability, which looks quite promising. I'm not a pro and may never get there, but have spent plenty of time with "real" artists. It's not a competetive sport and most, who are also real, live human beings, are encouraging of each other and especially of beginners. At least ones who don't already "know" everything... And you strike me very much as someone not in that category. A little humility goes a long way in life, eh?
Take some deep breaths before you go in, think of 17 year-old me taking that robe off for the first time and have fun! Look forward to seeing more of your work.
