Ron, I am sure not an expert but what the prevuious owner did sounds pretty good to me. A simple test for if the floor is protected is to sprinkle some water on it. If the water beads up and doesn't soak in, it is protected. My guess, without seeing it, is that he used a flat poly. You might want a shinier finish but too shiney a floor is an invitation for a slip and fall accident.
To try answering your questions: Do everything possible with a rotary motion on a parquet surface like sand and screen.
A lambs wool applicatior works well with Polys.
Sidebonding is bonding one tile to another, like grout with tile.
With any finishing project, you have to give the surface a "tooth" for the new surface material to stick to it, therefore, screen with a rotary floor polisher before applying a new finish.
I saw your second post but don't remember all the questions there but the Helmsman product is a good one. I would sure use this if you must put on a gloss finish. By the way, the only difference between a gloss finish and a matte finish with most paint/varnish/lacquer/poly type products is simply the amount of talcum powder in the can. Yep, plain old drugstore talcum powder. Henry in MI