Pleased to hear it went well
5 quid a session's pretty good (assuming a decent instructor, of course !) - where I go (my localish gym - N surrey/Greater London) it works out about 6 a session, for a block of 5-7 sessions, as a member - but double that as a non-member. I don't think I'd get *too* worried about class size unless it's all beginners - a decent instructor will probably just keep a bit more of an eye on the beginners and a bit less on the more experienced bods... tho' ours seems to have eyes in the back of her head
YMMV, but half-dozen or so sessions is probably about right to get to grips with the breathing and body-awareness elements - it's not unusual to hear beginners not finding it doing anything, but it's usually 'cos they haven't worked out what they're doing. There's different versions of each exercise according to ability/injury, so there's always a challenge of some sort - and even some of the basic exercises can be as good as -or better than- the supposedly more tricky ones if you focus correctly.
The class I go to tends to be the less circumferentially (?)-challenged...mebbe just we're a bit more aware of putting on weight than anything, not everyone is a member of the gym it's held in. You're certainly not going to lose much weight doing Pilates but it's a good complement to other activities - and the improved body awareness helps with balance and posture. Certainly kept me ticking over when I had 3 or 4 years of not doing much regular cycling or other gym work.
In theory our class is about 16 or so but at any point about 10-12 turn up - there's usually 2 or 3 of us blokes nowadays - we're mostly (nowadays) in the 35-55 range but most of us have been going for 5+ yrs (about 10 in my case) - it's an improvers/advanced class - not so much ability, so much as we all know what we're doing, we occasionally get relative beginners and they cope fine.
At least a few have come to it from having back injuries - as did our instructor, who was badly injured in a car crash when she was younger - IIRC expectations were she'd never walk properly again. Dunno how much of a recovery she'd have made otherwise - she was an aerobics instructor already - but you certainly wouldn't know it.
>I doubt I'll ever be best friends with my pelvic floor,
I must admit without the anatomy (or at least, active anatomy) to help identify it, it's a bit tricky. Our instructor uses the 'lifting a towel' analogy..which is ok if you currently have an..erm...towel rail to hand. And I don't think assisting in that department is part of the session fee...