straight into a demi john, a bucket isn't neccessary because it's filtered juice and there's no straining to do. you'll need to rack it off once fermentation has finished, I usually just wait for it to ferment and clear in the first vessel. cold water is fine, but if you can get it closer to room temp any way, that might be a better option as the yeast need about 20c to ferment. maybe boil the sugar in 1L water to dissolve, and make up the rest with cool water - just don't pour boiling water into the demi john!
you can switch out the cartons for whatever you like really. One grape is probably worthwhile, but most combinations make Rosé by accident because red wine is hard to make on a home brew level without expensive kits or real grapes - white grape and pomegranate, red grape and blueberry, etc...make what you like. the standard rosé is pretty great though!