There's an October S&B?
I think it would be feasible to do a jam club - but it might be better to do a Saturday or Sunday afternoon rather than an evening, so that there's time to get back from A&E and scrape stuff off the ceiling before you go to bed. On which note I think drinking and jam-making don't mix, too much scope for bad accidents. Although a spot of alcohol in the jam before it goes in the pots... (not Baileys, ideally)
The thing about warming the jars is partly so that they don't crack when you put hot jam in them - to be on the safe side I only turn the oven on (to like 1/2 a degree) after I've put the jars in.
Also I think it'd only be possible to make one batch of jam really, otherwise it'd get complicated and time-consuming and there wouldn't be space (preserving pans are BIG). Preparing the fruit can take ages, eg peeling and chopping loads of apples, but blackberries for instance just need a wash and picking out the dodgy ones.
I'm not really a jam expert, I just follow the recipes, more or less. It's all about pectin (it says here) - pectin is like gelatine, it's the stuff that makes jam set, and some fruit like apples has lots of it and some doesn't, eg strawberries. So if you're making jam with fruit that doesn't have much pectin in you have to add another fruit that does. Lemon is a safe one that does so you can always just bung extra lemon juice in, which improves the flavour anyway IMO. The special jam-making sugar zenie mentioned is special because it contains extra pectin, but you only need that if you need the extra pectin. Anyway you don't really need to know all that if you just have a decent recipe to follow.
Then there's getting it to "setting point". There are various tests you can do to see if it's ready, eg the wrinkle test where you put some on a saucer and let it cool right down, then push your finger through it to see if it wrinkles (if it does it's supposedly ready). Personally I tend to do it in two stages, make the jam one day, then leave it in the pan overnight and bottle it the next day, so that I can check whether it's really the right consistency when cool.
I've actually still got loads of that batch that Mrs M had some of - it was blackberry apple and banana, and I overdid the banana I think, bit gloopy.