How does this compare to other Mt. Baker routes?

The North Ridge of Mt. Baker is one of the more challenging routes that are commonly climbed on Mt. Baker. It features more consistent steepness and the crux requires some steep ice/snow climbing skills so it's not a beginner route like some of the others.

Are there other North Cascade climbs that would be good to do before this?

There are great climbs all over the Cascades that would be good as a lead into the North Ridge of Baker Climb. Fisher Chimney's on Mt. Shuksan would be a good easier route and the North Face of Mt. Shuksan would be a bit harder. Other climbs like the West Ridge of Forbidden or S. Ridge of Torment might be comparable in physical output but are different in terms of technical difficulty since they're more rock climbs.

How fit do I need to be for the North Ridge of Baker climb?

It's more of a marathon than a sprint. In terms of other Cascade climbs it is not the most difficult but it's pretty high on the list of challenging routes that are on a lot of climbers tick lists. You should be able to move through steep terrain efficiently for hours at a time. If you haven't done a 10-12 hour day in the mountains we would recommend that prior to doing this climb to see how you feel.

Do I need to already know crevasse rescue skills before booking?

If you don't have prior glacier experience then we might recommend a 4th day so you can spend the first day focused on those skills and feel confident in your rescue abilities (it also makes the guides feel safer). Even in a 3 day trip we like to start early and work on some glacier skill refreshing prior to the summit day which is almost entirely on the glacier.