When I cited the table for spoke lengths in their manual, that was the 32 spoke chart. This link is newer, you should use this table that has both 32 and 36 spoke columns.
http://www.rohloff.de/fileadmin/rohloffde/technik/speedhub/speichenlaengen/erd_32_36_Speichenlaenge_07_2015_de_en.pdfI looked up my original order for spokes, I bought 232mm spokes for a 36 spoke build. The Rohloff table says that spoke should be used on an ERD of 535 to 538.
Even if the rim is 541 as cited by SJS, that would mean my spokes are only off by 2mm, and a spoke that is 2mm too short is not a big deal. (Too long and you might run out of threads before you get it tight, that is a big deal.) I just looked at my wheels, the front looks like my spoke length is right on but my rear wheel looks like I might have about 2 mm of spoke threading outside of the nipple on the rear wheel. See attached photo. So, I probably could have used 234 mm spokes and that spoke would be about right for a 541mm ERD according to the Rohloff table.
So, to summarize, my rear spokes might be 2mm too short, but my front are right on. Not sure how to interpret that when it comes to back calculating ERD. (Fortunately, my bike works fine so I do not need to worry about this stuff any more.)
I previously suggested that you order your spokes with the hub since the spoke length is odd for a Rohloff and Rohloff sells packs of spokes to make it easier to find the spokes you need. But, I am starting to think the best thing to do is to buy the rims you want and ask your wheel builder to measure the ERD from the rim. That takes more time, but you have the time.
Some bike shops have a spoke threading machine and can make custom length spokes. I used to buy my spokes from a local shop, they commonly cut to length instead of maintaining a large inventory of spoke lengths. I used to bring my hubs and rims in to them, they would measure ERD, calculate length, and cut and thread my spokes for me.
Regarding the angle of the nipple at the rim, that is why I used Sapim nipples on my Nomad. I checked my order form, I bought 12mm nipples. Sapim claims that their nipples are better for getting those odd angles on the rim. In the photo you can see I do not have a lot of nipple sticking out of the rim, but there was enough to get my spoke wrench on it.
http://www.sapim.be/nipples/brass/polyaxI used Wheelsmith spokes, in part because I always use their spokes. And Peter White likes them, that is a pretty strong endorsement. They sell their spokes in bags of 50, so I have more spares than I could ever use. And the Sapim nipples came in a bag of 100.
In USA it is very hard to find Sapim spokes, so I did not spend a lot of time looking.
I use the green spoke wrench on the Sapim nipples.