Steerer length is the critical fit dimension, axle to crown length should be pretty close to what you're replacing if you don't actually want to change the geometry of the whole bike, and fork offset should match what you had before or you'll change the steering geometry, although that's not all that critical unless you're already on the edge of the envelope.
Really though, you probably shouldn't even be replacing a threaded fork, threadless is superior so take the opportunity to upgrade with a new headset and stem.
Yeah, why not. After all, you're only entrusting your life to the most highly stressed part of your bike, and the one whose failure is most likely to result in your death. What could possibly go wrong?
Steerer length is the critical fit dimension, axle to crown length should be pretty close to what you're replacing if you don't actually want to change the geometry of the whole bike, and fork offset should match what you had before or you'll change the steering geometry, although that's not all that critical unless you're already on the edge of the envelope.
Really though, you probably shouldn't even be replacing a threaded fork, threadless is superior so take the opportunity to upgrade with a new headset and stem.