A few things to ask when considering a gig:
Is there a place to change? Coming in to the room in a bathrobe and then dropping it to pose is a lot easier than having to strip off your clothes in front of everyone.
Is it going to be warm enough? Are there heaters available?
How long would your shift be? What sort of frequency/duration of breaks? Standing still is much, much harder work than you’d think.
Is the teacher someone you feel you can trust? The teacher is to some extent responsible for your comfort, so if the teacher is an annoying jerk you’re less likely to have a good experience.
How long will the poses be? If the teacher just wants gesture drawings, you’ll be doing poses from 10-60 seconds. If the teacher wants more completely rendered drawings, you’ll be doing 10-30 minute poses.
As for posing, try a few poses at home. (By “pose” I mean staying still) Most long poses are done seated or lying down. Short poses can be much more varied. But don’t overestimate your staying power. I was drawing a model who kept trying “warrior poses” because he was into martial arts. Thirty seconds in, he’d start to waver back and forth (making him really hard to draw) and a minute or two in he’d give out and have to abandon the pose.
Also, don’t worry about your body type. The group I was drawing with was always clamoring for interesting bodies. We wanted folks with rolls of fat, with wrinkles, with interesting details to draw. We got one guy who was just…well, he had no muscle tone, and no real body fat…he was completely and totally smooth. My friend dubbed him “Marshmallow boy” because there was absolutely nothing to draw on the guy. (He didn’t even have body hair)
Err, that’s not exactly encouraging, but at least we were frustrated with him for artistic reasons rather than aesthetics.
If you do decide to pose, just count yourself lucky that you’ll never have to worry about one male model’s problem. He simply could not make up his mind if he was excited or not. It was up, it was down, it was up, it was down. I wanted to yell “Just go in the back room and take care of that thing so it’ll lie still!”
Okay, so that wasn’t a particularly encouraging anecdote either. Sorry.
As for objectifying nude models, isn’t that sort of the point? When I draw nudes I treat them like statues. Afterwards, they’re regular people, with no awkwardness at all. But while they’re posing, I fully intend to objectify them.