I actually like the idea of setting it during the Aiel War, although you're going to have to figure out if you want to allow PC Aiel, and if so, can they "defect" to play with the rest of the playerbase.
I think that you're right about needing some flexible timelines, but I'm not entirely sure why you wouldn't let people start as Blademasters if you'd let them start as Aes Sedai--the power available to a Blademaster is minimal compared to that of an Aes Sedai.
There are a couple of ways that you could handle channeling under Ares, ranging from the simplest (Channeling skill and "weapons" based off weaves, everything else just RPed) to middle of the road (Saidar and Saidin skills, weapons based off weaves, and a compendium of rules for other weaves like we did on The Fifth World), to the more complex (Saidar and Saidin skills, weapons based off weaves, compendium of other weaves, and an added system for channeling weariness).
I agree with the idea that if you have Traveling, you can have grids all over the place, but I would definitely still focus things on a single city (or a single city plus Tar Valon, because you know that people will want to be Warders and Aes Sedai), just have micro-grids for the other cities.