Whilst I would agree that it would probably be better to have the bridge north start and finish wires taken to ground instead of commoned up to the hot output, practically it is impossible to arrange (as far as I can see) with that particular on/on/on DPDT switch selection and still have the parallel wiring option. Practically, it works just as well, as the two ends of the north coil are shorted together (albeit connected to signal hot), so no output can be developed by that coil, so you only get the other coil's output signal.

I can say from experience that it's certainly a good thing to have the slug coil of the bridge pickup selected as the coil split (provided the humbuckers are in 'standard' arrangement with the screws facing outwards and the slugs towards each other). Mainly because it's that bit further away from the bridge itself so the sound is fuller and has less of a thin sound to it than the screw coil. The screw coil normally ends up slightly closer to the bridge than you'd normally position a single coil bridge pickup. Even a few mm can make a big difference to the sound in that area. The nearer the bridge, the smaller the amplitude of the fundamental and first few harmonic string vibrations, so almost no bass end to the sound and you just get all the higher pitched harmonics.

Sound-wise, it's personal preference as to which coil you have split for the neck position, but if you want the mixed split position to be hum cancelling, then the selected coil has to be RWRP with respect to the bridge coil, which (as long as the pickups are from the same manufacturer) means that if the bridge is the slug coil, then the neck needs to be the screw coil.

Despite everyone showing similar north/south start/finish diagrams and telling you which of the signal wires should be connected to ground, I've found that there's about a 50/50 split between manufacturers as to the signal output polarity if you follow their recommendations.

So if you want to be sure that you select the slug coil or screw coil of a pickup, you really need to do a temporary connection to an amp of the wire pairs of the pickup.

Use a multimeter to work out what the pairs are. The wiring diagram should indicate the suggested ground and hot wires ('suggested' as you can happily swap them over if necessary) indicating the wires at one end of each coil, so it's just a question of finding out which of the other two wires is the other end of each coil. Then write it down!

Having a 'test' guitar lead with crocodile clips on the end is always a good idea if you do a lot of guitar & bass pickup work, but if not, I'd cut a jack off one end of the (really poor quality) kit lead, bare the wires and use a bit of 'chocolate block' terminal (or similar) to connect pairs of pickup wires to the amp set to a quiet volume. Tap the slug and the screw poles with a screwdriver and you should hear a big difference in the resulting 'click' sound for the connected coil. Again, write it down as a reference as to which are the slug and which are the screw coil pairs.