For the few Ao100 I played atm, I always went for scavenger.
WK 2 looks like a must have for such a run, and I think Int2 is a good investment too.
I don't "rush" the mastery, though, since it's not immediately useful, but improving chances of getting good mods, and thus, becoming overpowered, is THE best way to go.
Also, I hope something will be done to make it able to use not only armors, but also melee weapons... and make the dissasembled mods less random, e.g., by tweaking weights of mods depending on what has been already obtained with disassemble. Currently, with some bad luck, you won't even get one nano in 100 levels, which doesn't look normal to me.
About ammochain, I think it's overpowered (AO100 or not). What would people think of using 2 ammo per volley ? I'm sure it still would be one of the best available traits.