For some reason when I have activated a number of mods, when I want to activate another one, they randomly stop working some of them, and I don't know what to do to make them all work at the same time. At the moment I have my list of mods like this and I haven't added more because of that problem.

A list with all working mods on patch 1.6 can be found here (scroll down a bit):
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Voobly can only loadtoo many mods. Likely that's what's happening.
Take the mods that never change, like the grid or the trees, and combine the contents of their folders into a single one. See the last part of this page:
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I need a mod for Land Nomad map, so no one gets huns.. is it possible to get such a mod? Can i do it by my own? How?

There's no way to influence the random civ selection. The obvious solution is to pick civilizations, even if you sample tem with an external tool.