Re: Pickup Height
The one thing to look out for is raising the pickup too close to the strings or you can get "Strat-itis".
This is far less of a problem with standard humbuckers or any pickup with a bar magnet because the magnet itself is much farther away from the string than with Strat/Tele pickups, but you can get a touch of "Strat-itis", especially with stronger magnets like Alnico 5 and ceramics.
Strati-itis is much more of a problem with neck pickups because less force is required to move the string the farther away from the end of the string you get. This is why you will find that conventional wisdom has the neck pickup a bit further away from the strings than the bridge pickup.
You lose some bass and upper mids when you lower the pickups but the treble is sweeter and more chimey. The pickup becomes more rude in the midrange as you bring it closer.
Keep in mind that raising or lower the pickup DOES NOT HAVE THE SAME EFFECT as raising and lowering the pole pieces. Adjusting the poles does alter the magnetic field, but it does not affect the position of the magnet itself.
Pole piece adjustments give you more subtle results and in the case of your standard humbucker where only one coil is adjustable, raising the poles will add brightness because it makes it sound a touch more single-coilish by emphasizing one coil over the other.