Linoleum underlayment removal
Linoleum can be a total bear to remove in and of itself. If the substrate is screwed or nailed down then it shouldn't be too bad but if it's glued to the sub-floor then you're gonna have a bad time.

If I had to guess then there might very well be hardwood flooring beneath the linoleum which may have been sanded down to accommodate the linoleum's thickness. If this is the case then ripping up hardwood flooring isn't too difficult unless it was glue down.

As you can see, without knowing what your substrate is, it is impossible to know how big of a challenge you have ahead of you. There could be several linoleum layers for all we know.

So:

Step #1: remove at least one piece of linoleum from an inconspicuous location such as a pantry or closet since you might decide F*** it after all

Step #2: take a picture of the substrate and edit it into your question

Step #3: you probably won't need someone here to tell you how difficult things are going to be as you'll have a general idea of what you are up against