We have a rather nice mahogany dining room table that is beginning to need
refinishing after 30 years of reasonably careful use.

I'm thinkng of doing this job myself. I have a hand sander.

A few questions:

1. Do I need to remove the old high-gloss varnish before saning?

2. Is sanding likely to significantly change the color of the wood?

3. If it does, can I get a stain that will restore it?

4. After staining, should I apply several coats of high gloss polyurethane?

5. How do I prevent, bubbles, which I've gotten in the past when I used
polyurethant?

Any guidance appreciated.