Well, I've now returned to the Sheaim to try out the advice found here. Now that I understand the real value of the planar gates, I'm getting my own force of marauders and Mobius witches, which makes quite a difference.
It's still a bit of a struggle to get established. I'm researching up to Knowlege of the Ether together with some basics (agriculture, education, exploration etc) and festivals to start, but I'm finding I still need some luck as my warriors often seem to have the life expectancy of a soap herring. Once KotE is done, I try to use adepts in place of warriors, so they get the xp, but when the infrastructure is still in its infancy, the loss of an adept hurts a lot more than a warrior! These pressures ease considerably once summoned units start appearing from the gates, but that makes for a pretty fragile start.
One idea I've been trying out is to nab Warfare and the Form of the Titan early, for the xp bonus, assuming I can get a unit up to lvl 6 by then (a lot easier with Tebryn than Os-Gabella, since adepts will naturally grow in xp faster anyway, though they'll still need some "field experience"). In retrospect, I wonder if this is worth the effort, since I don't think summoned creatures (either from a planar gate or by spell) benefit from it, much like they don't benefit from apprenticeship. Adepts do however, so if I usually treat them to Combat I strait out of the guild. I still have a nagging suspicion I could be spending my time and effort better on something else. Anyone care to offer an opinion?