I just thought I'd pop up and say hello - I'm the other half of the project (not entirely true... Emma has promised to help with scenery). Seb is the man behind the rules, and has to put up with me spamming him with ideas (good, bad and bizarre) of modifications. A good example are the weapons options - the crossbow pistol only made it to the list because I have a few figures armed with them, much to Seb's annoyance (?). [As pointed out by the late, great Sir Terry Pratchett, pistol crossbows are for posers -- Seb]
I've been dabbling in PA wargames for the last 15 years or so (general wargames for a few more), and as time has gone on I've leant increasingly further away from the classic Mad Max/Fallout/Zombie tropes. My last project was 'WinterApoc' - a UK set (and thus low fire-arm density) gritty setting, visually inspired by The Road.
For ATR, I am planning a force of 'northern' nomadic raiders. I'm drawing heavily on some of the descriptions of the nomad empires from Philip Reeve's World of Mortal Engines book series. The general asthetic will be cossack-meets-Rus-viking, although I am shifting the emphasis heavily on to infantry. With war-mammoths (and possibly war wagons - although I haven't spoken to the man that writes the rules about that yet...) The nomads have a black-powder technology level; so expect savage warriors with hand axes and firelock muskets supporting the heavily armoured retinue of my warlord (lots of chainmail and pistols...).
Hopefully that will give some sort of introduction!