1. A lumber company or mill wants the wood for milling and sale. Fine oak
wood might be somewhat scarce in your area, or perhaps they have a portable
mill that they can bring to the site and simply want to put it to good use.
I would ask for 3 references from other people who have had trees removed by
them.

2. Oak roots won't sprout in perpetuity after the tree is cut down, but it
would be a good idea (and certainly as part of the 'free' service the lumber
company should grind the stump to below ground level.

3. Your quotes sound reasonable, especially if climbing and rigging is
involved in bringing the tree down.

Dave