Not sure about the part number, but I can fill in the rest.
2. Pretty cheap. I think I picked it up on Ebay for around 40.
3. Slight increase in power on the freeway, little bit quicker throttle response. Need to clean mine out again...
4. No real change in the milage.
I would look at getting a generic synthetic instead and just doing a short ram conversion. The synthetics can be cleaned with water and don't have the 'must be dirty to work' deal going on with them. But you can't beat the K&N for ease of install.