I need to re-read Scriveners Moon to get the details of the descriptions of the Northland Nomads (specifically Clan Morvish of the Arkangelshk) so this is a definite work in progress... I got the impression of the majority of the Morvish warriors being 'hairy northern barbarians' types in furs and chainmail, armed with aquebuses, pikes and bows and riding to battle on mamoths. To me, this and their nomad life style, conjurs up images of a mix between cossacks and vikings or Rus. The use of War-wagons is also a bit cossacky, however the people who are most famous for them are the Hussites, so I'm going to try to incorperate some elements of their attire and look into the concepts.
A common feature among all these types is a long (knee to thigh length) tunic/kyrtle with trousers underneath (some of which may be baggy, and tucked into high boots or leg wraps). They also have a tendancy towards beards, lots of hair and furs. Given that the Northlands are cold, lots of coats and cloaks will probably be warn, although in some cases this might also be combined with armour (either padded or leather).
On the subject of armour, chainmail is specifically mentioned in the book and was a feature of both cossacks (until the late 1600's) and vikings. Chainmail is typically a product of a society in which manpower is cheap and dispersed, but resources are tight. Plate mail requires a lot of experiance and good qulaity metal to prevent it cracking or being too heavy to move in; whilst scale or chain armour can be produced by blacksmiths, given enough time. Definitely suitable for the nomads in the books! Helmets aren't mentioned, so I have lattitude to use Spangenhelm vareints from Rus figures, alongside medieval pot and kettle helmets from hussite figures. In terms of other headgear, fur hats seem obvious, as do 'floppy' hats.
In terms of weaponry, arqebus', bows, pikes and swords of an unknown type are mentioned in the books. It seems a fair artisitc licence to add muzzle loading pistols, maces and axes to the mix. The swords poses the greatist disparity between the various possible sources of figures. I'd like the swords to match to add to the feeling of homogeneity, but I don't know of any sources of curved sabres, so I imagine I'll be using strait swords. I've no idea what sort of shields to use, or even if I should use shields. If I don't, the vikings may look a bit akwardly posed, if I do, then I'll have to convert some cossacks to hold them (which may make some of the cossacks look awkward, but may also look good. It's hard to tell). I think square shields would look a bit different compared to round shileds and further differentiate tham from vikings...
Luckily for me, these ideas also open the way to being able to use some early wild west frontiersmen, with a little modification (cutting off tassles, adding furs, changing head gear)... I'm sure there'll be more musings on this to come!