important: 

The rims seem appropriate for your purposes, as they are described as providing a benchmark on the touring and trekking market. The hubs also seem fine. The spoke length will depend on how you decide to build the wheels.Believe it or not, when I started racing, the standard was 36 spoke 4-cross wheels. Spokes were double butted and the tubular rims were very thin and light, so that helped a bit wih weight. Those wheels were bullet proof. Now the 'standard' is 32 holes for most purposes. The cross pattern is all over the place, mostly 2 cross and straight laced for racing wheels. Whereas front wheels are symmetric, rear wheels are often laced differently on drive and non-drive sides. This is due to innate asymmetry in the length and load placed on the two sides of the rear wheel, which is not symmetric due to the cogs on one side.

If you want to be bullet proof, then I would recommend 3-cross and 32 spoke. If you are worried about your weight or you want to use panniers, then you could go to 36 spoke on the rear wheel. I believe this is standard for tandems.

Once you figure all that out, then you should call the store that you want to buy spokes from. Tell them your hub/rim combo and lacing pattern and they will pull out their spoke calculator and figure out what length to sell you. Even if the lacing pattern of the rear wheel is symmetric, the length of the drive side spokes will be shorter than the non-drive side. The tension on the drive side will also probably be higher, but that depends on the precise length used. 

A dishing tool and truing stand are helpful, but not actually essential. You can make sure the wheel is centered by putting it on your bike and. Use the brake bolt to define center and use the brake pads to detect when it is out of true. Start out by adjusting all the spokes to the same tension (pluck them and make sure they all sound the same pitch). This will more or less center the wheel. Then gradually tighten. You should put blue lock tite on the threads so they don't loosen up over time.

It really helps to have another wheel next to you as you lace the spokes. Just follow the pattern. Otherwise you have to think a lot. 

I'd look into some wide rims.  Especially if you have wide-rimmed race wheels.  I have a hard time believing you'd have a problem with a decent mid-weight rim and a 23 to 25mm tire pumped to the right pressure.

Not sure why the XT hubs are your preference.  There are lots of good  hubs out there.  Front hubs can last forever.  Rear hubs have the problem of extra load, changing cassette standards, and more pieces to wear out.  I'd probably skip XT because I'm not sure if they're 11-speed compatible.  I'd also suggest going with something that has a cassette body which can be swapped for Campy just so you've got as many options available.  

32 spokes 3-cross or 36 4-cross are hard to go wrong with.  

Double-butted spokes work great--as a friend said, 'spokes never break in the middle'.  Straight-gauge are cheaper.  Feel free to mix and match--lighter spokes on the front with heavier in the back.  I've frequently used 14/17/14 on the non-drive side with 14/15/14 on the drive side, or 14 straight on the drive with 14/15/14 on the non-drive.

Brass nipples over aluminum.  Brass are typically 1g per and alu can be 1 or 2 g for the set.  They can hold equally well, but alu rounds easier and is more likely to pull out if yanked by a pedal or stick.

In terms of quality, DT and Sapim are considered the best.  Wheelsmith stopped producing, but if you can find them, they're as good.  

There are countless online spoke calculators. Just look up "spokecalc"

The Jobst Brandt book is the bible.  But Sheldon Brown's website has advice that works fine.

 

I would not go cold turkey on wheel building. 

Perhaps these guys might teach you http://ifixbyx.com/site/

In terms of durability, I have a 10 year old 32/36 straight gauge spoked Mavic Open Pro on my round town bike, still round and true. Although it's true spokes don't break in the middle, I'm not a fan of butted spokes as they tend to flex more, potentially twist more (unless you have a good wrench truing your wheel) and get out of true more easily — straight gauge just makes a stronger wheel.