1) Usually deffo the inner coil, which should be the slug. The screw is closer to the bridge where there is less string movement, so even brighter and less powerful sound.
If you go split you might wanne consider adding a 2k resistor in series with the split path. This is often refered to as the PRS style split. What it does is that the coil is not completly turned of by entering a resistor that works as a static volume pot you can just switch in. That way you retain a bit more power and fullness. Nothing groundbreaking, but worth it imho.
2) Series/Paralell is something a lot of people swear by as an alternative as it stays humcancelling and also gives single coil-ish sounds. Also more balsy than splits usually. My experience with this is limited thus far, but it is on my list of things to try more for the future.
Thus far I was more of a split guy myself, but note that I only use the split alone with my Crawlers, which are known to split superbly. On the other guitars the split is always activated automaticly in certain positions. On the HSH it is in 2 and 4 together with the middle single coil and on the HH I use Petrucci style auto split middle.
Will soon rewire one neck PU for series / parallel and as soon as I get some more push pulls I will probably mod 2 necks and 1 (maybe 2) bridge(s) that way as well.
If you are not combining the split Ry bridge with something else I would recon the series / parallel would be better for you. However you can never really tell until you tried it.
