Re: New vinyl over old
You can overlay any vinyl that is still solidly adhered to the floor, even if it's worn through or has chunks missing, as long as it's solidly affixed to the floor you'll be alright.
You'll want to get some floor leveling compound, this is a dry product that you'll mix with water to about the consistency of pancake batter. This gets thinly skimmed over the surface to fill any voids or embossed pattern of the old floor. Before it fully cures (still slightly soft ) you'll sc**** your skimming knife over the floor to remove any ridges or lumps. If necessary, apply a second coat, or touch up deeper gouges if need be. Basically, any irregularities here will telegraph through the new vinyl. Once completely cured, give it another light scraping. Sweep up the big debris with a fox tail broom will do fine, better would be to vacuum with a shop vac, and you're ready to lay the new vinyl.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!