Hi Sam,
WRT the crank, I think the Orgin8 will work, but getting it to the proper Rohloff 54mm chainline will involve finding the correct bottom bracket. The crank you're looking at on eBay appears to be Origin8's (house brand of J&B Wholesale) single-speed model listed here:
http://www.origin-8.com/?page_id=91&short_code=Alloy+Crank+Arm+Set&prod_model_uid=1006&cl1=CRANK+ARMS+%26+SETSAndre went through the BB sizing dilemma here:
http://www.thorncycles.co.uk/forums/index.php?topic=3898.0 You may find his journey helpful.
A possible consideration...
I haven't seen the back side of this crank's mounting spider, but if it is truly a single-speed, the chainring will only mount to the outside. I'm not sure if you'll be running a bash guard/trouser guard with your crankset, but this might be a consideration if you do. Usually, a double or triple crank is used in that case, with the chainring mounted to the inner lands and the bash guard to the outside. If you do go with the SS crankset and later wish a bash guard as well, it can -- depending on crankarm/chainring clearance --be mounted with longer chainring pegs/sleeve nuts and spacers.
As for the Abus Amparo, both Il Padrone (Pete) and JimK used the CL nylon bands in mounting Amparos to their Nomads. Jim generously included some very useful photos and measurements of his Abus Amparo 4850 here:
http://www.thorncycles.co.uk/forums/index.php?topic=4148.0 These should help. The basic mounting strips will work fine and have the added advantage of keeping the lock within the rear triangle.
Here's how the mounts break down:
CL - Supplied with universal attachment clips for those bikes without any factory installed mounting points - Most of these are "NKR", meaning the key can be removed when the lock is open.
LH - Simple screwing to existing frame mounting points on the seat-stay down tubes or can be installed with supplied self-drilling screws - Key cannot be removed when lock is open <-- Avoid this model for your Nomad.
SP - Mounts to the seat-stay bridge existing mounting point with supplied bracket - Key can be removed when lock is open
This photo clearly shows the difference between the mounts:
http://lockitt.com/mm5/graphics/00000001/abus-amparo-4850-7002.jpgThere's actually a fourth mount available to place the ring-lock on the v-brake mounts, a bit less secure because it is outside the rear triangle.
If you go with an AXA Defender as I did, be prepared to modify the available ATB mounts to make it fit, as the Nomad's 19mm stays are too large for the stainless steel worm-drive mounting bands that are the default for that lock. I have instructions and photos for modding the AXA Defender mounts posted here:
http://www.thorncycles.co.uk/forums/index.php?topic=4987.0 A "key" reason I went with the Defender was to get the seatstay mounts with a key that remains in the lock when it is open so I cannot leave it at home. The key only removes when the lock is...locked.
I think the Abus Amparo 4850 has it all in terms of quick and easy mounting to the Nomad, and as for security and convenience, it is pretty much a wash, with the Amparo having the added benefit of a bit more clearance for the tire at the lock's entry. I would choose the Amparo if I wished to use tires
wider than 2.0in.
You may wish to consider purchasing a plug-in cable or chain as well. They are very handy for securing the ring-locked bike to a stationary object and/or helping to secure the front wheel. Any regular cable can also be used, secured between the ring-lock's tang and the wheel rim. From a security standpoint, a ring-lock is not the most secure of locks, though it is among the most convenient. I would strongly suggest adding a U-lock for parking in overnight or in risky areas.
Hope this helps.
Best,
Dan.