if it's getting too wet/smelly from the food waste, you may be adding too much at once, or too much in one spot - try 'aerating' the bedding regularly for a while by stirring/lifting - the sour smell will be an excess of unused feed that's decomposing anaerobically - slow down on new additions

don't know why you'd freeze or nuke the compost, unless you mean the waste material before you add it to the bin, and that's not at all necessary, especially when you consider that worms eat actively decomposing material because their real food is the microbial life on it, and pre-treating the waste will kill off any microbes that happen to be present, meaning it'll take longer for the material to become attractive to the worms

if the bin is really wet, yes the cardboard will absorbe enough moisture the worms will eventually work on it - they seem to be especially fond of the glue!

note also that the worms prefer too wet to even the slightest bit dry - their little bods are largely water, and in a dry environment that moisture gets sucked right out of them

Bill