I would destem, wash, halve & pit, then put 'em in gallon size Ziploc bags to freeze solid for a few days. Freezing helps to break down cell walls in the fruit, which means more juice & more flavour from your fruit. I'd leave the skin on the fruit, it'll add some flavour & they'll likely slip off when you mash the fruit (I use a potato masher) anyway.
I wouldn't heat the fruit at all, I'd just use sufites. It's a lot easier, you don't risk setting the pectins & you don't drive off any flavour. You can (and should) use warm water to bring the fruit/must up to pitching temp though. Regards, GF.