Hi Johan,
Sounds like a cool project. Alder body and maple neck/rosewood board is a tried and true combination. My favorite stage guitar has this wood combination, too.
If you buy from BKP I would go for the 280k pots, both volume and tone, and a 0.022uf Jensen BKP cap. However, 250k pots will work just as well - the difference in gain will be negligible - so will be the difference in highs. I used the BKP 550k pots for a humbucker guitar and they are just very, very good quality.
As regards switching - the standard three way slider is cool enough for me because it is very easy to handle. The Fender four way switch adds a position that puts both pickups in series instead of parallel which gives you a sound similar to the "both pickups on" position but darker and hotter. I put this into a Tele but found I never used the series position. Craig Anderton has devised a very cool switching scheme using a standard five way switch instead of the three way switch, giving two more sounds to the three standard sounds. Tried it and found I did not use the two extra sounds either. And of course with a multipole switch you can come up with any pickup combinations conceivable - sometimes at the expense of practicality.
Hope that helps.
Cheers Stephan
