Doors and Windows - Painting Old Double Hung Windows

I'm currently sanding all of the old stain of the interior part of 90-year-old double hung windows, so I can paint them white. Any suggestions on the process?

Do I need to re-caulk around the glass?
Should I use a primer on the wood before I paint? If so, what kind?
What type of final paint should I use?

The interior of a wood window does not have to be caulked. What weather-proofs a wood window is the glazing around the glass on the outside of the window.

The best way to sand and paint a wood window is to remove is from it's casing and do it. One of the most common window problems is painting them while there in. Paint is a very good adhesive and painting while there in usually binds them in place. Making it difficult to open and close.

Since you're sanding the stain off, you have to use primer and then paint. Any type of interior trim paint will do.

You may want to check out http://windowrenu.com and it gives you some insights about windows that you may find helpful.

I have no problem with what resercon told you, but, after you go through all of that, you STILL have windows that are as inefficient as they were 90 years ago. Have you looked into retrofitting them and making the energy efficient? A lot less work, virtually no future maintenance, cut your utility bills by 25% to 50%, and you may get a rebate from your local utility co. (Just a thought!)