Re. the moldy smell in the vacuum: Probably the hose. I'll bet it picked up something wet at one point, and that did it. Try running it without the hose and see if the smell comes back, and if not, replace the hose.
Re. compactors: First, put your wet sticky food waste down the disposall as far as possible. Second, if you have wet drippy stuff that's not food waste, do this:
If you get milk or other beverages in cartons, when you're done with one, give it a quick rinse by shaking about 3/4 a cup of clean water in it and then pouring it out. Now open up the top of the milk carton. This takes less than a minute. Now you have a nice little container for wet drippy stuff that won't go down the disposall. When it's full, fold over the top and toss it into the compactor like anything else.
Luxflairguy's info is good. Also do this: When you have a bunch of wet sticky stuff in there, put a layer of something dry on top before compressing the load. For example a single page of newspaper folded normally, or one of those junk mail flyers. (Your recycling bin won't miss an occasional piece of paper.) This will at least keep the wet stuff from clinging to the compressing ram. BTW those things probably generate about a half ton of pressure so they should be treated with due care.
A removable ram cover would be nice, but it would have to be fastened to the ram itself in some manner that was both secure and easy to undo to remove. This is not an easy design question to solve without creating other complications. Best bet is to wipe it down with a disinfectant such as a Lysol product or Pine Sol, or straight bleach, but check to see that the manufacturer says it's OK and won't cause corrosion or other damage to the equipment.
Last but not least:
A compactor may save you on the trash bill when the city is measuring your trash by volume, but measurement by weight is on the way.
How it works: a little barcode tag on your wheelie-bin, and a device on the refuse truck that reads the bar code and weighs the bin as the lifting mechanism is picking it up to empty it, and then the data get stored onboard the truck and automatically read into the city's billing system when the truck goes back to empty its load at the transfer station.
So get a compactor to keep your kitchen a bit neater or reduce your trips outside to empty the kitchen bin into the wheelie bin, but don't get one expecting to "cheat" on the city refuse collection rates.