1. Quote: "xDrive provides variable torque split between the front and rear axles through the use of a multi-plate wet clutch located in the gearbox on the output to the front drive shaft. This setup allows xDrive to modulate the torque split between the front and the rear axles, which is normally split at 40:60 ratio. If wheel slip is detected by the ABS/DSC system system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle."
http://en.wikipedia.org/wiki/BMW_xDrive
That means, if you drive aggressively enough, 60% of the full torque hit the rear tires, until the system decides to redistribute. Therefore staggered setup make sense. If you have your BMW with xDrive to commute in Eco mode, the square setup with the stock wheels is OK.
2. According to realoem.com and your pictures, you have the M double spoke 351 - 19''
http://realoem.com/bmw/showparts.do?...27&hg=36&fg=15 with the square setup of 8,5JX19 ET:33. With 8.5" both front and rear you can have the hubcentric 10-12 mm front spacer and 20-25 mm rear. Good site to know all about wheels and specs is tirerack.com.
3. The H&R springs provide 30-35 mm lowering, together with small vertical tilt of the struts the added camber is too small and can be disregarded. For the 19" wheels it is even less important compared to the 90% of people running 20" wheels and the rest running 21" (even 22") also with H&R or Eibach or ACS. However if you want to check it carefully, you can easily measure the gaps yourself, see:
http://www.m3post.com/forums/showthread.php?t=336209
4. The whole F10 body and suspension dimensions are the same. BMW itself makes a lot of confusion with model numbering, i.e. yours US 535d is our European 530d. H&R makes it even more complicated: their website says the sport sway bars fit only 2WD while it is confirmed they fit perfectly xDrive too. The only reasonable difference is the springs, because petrol and diesel engines have different weight i.e. axle load is different. Find an experienced local shop or BMW partner (also site sponsors) for guidance.
5. It's DIY 4 hours otherwise depends on the shop rates. 300-400$ and plus maybe alignment if necessary (not always).
6. Many of members here believe the proper wheels is the number one thing to do. Taking cost into account I would recommend looking at VMR, Forgestar, Avant Garde, Renn etc. (also check the Tirerack).
Hope the other members will chime in and give you more of helpful advices.