I have a new maple neck for a tele project. I want to tint it a bit, an amber vintage color, do I need to remove the frets first in order to tint / seal the fretboard?
No - you finish over the frets then when you dress them the lacquer gets taken off. If you're going to refret to a different size then I'd pull them, finish and glue the new frets in after cleaning the fret slots then dress them.
I assume you're only tinting the neck, not the fretboard right? If this is the case, just tape it off as mentioned and spray from there. If you're going to have a lacquered fretboard like a Rickenbacker, you need to check and make sure there is enough fret left to dress and crown the frets after you spray them.
In this case, if there is enough fret left, I would spray away, and when you're done, use micro-mesh to remove any lacquer that might be left after dressing the frets. Micromesh is also totally safe to use on the new sprayed neck, you just need to be careful not to remove too much lacquer from where you want it. Once the frets are dressed, start with a 1800 grit and work your way up to 15,000 grit. Your frets will shine like mirrors when your done. While you're buffing the frets, make sure you protect the fretboard by totally taping off the fretboard, or use a fretboard protector from a place like stewmac.com while you're buffing. You can find both products here:
Warmoth and Allparts seem to have a good selection and a lot of people say their parts are first rate. I have no firsthand experience with either but they look like good companies.
How about sanding between the frets? What is the method for doing that? I imagine it is very difficult to get the wood that is right up against the fret. Any tips?