[Alneyan]

Most of them aren't: only mods affecting a part of the game (like FQM for systems) can be used with other mods. PvK Balance changes Empire setup, but Proportions does that as well, and changes the actual balance between the characteristics; TDM requires the vanilla game to work, as it uses improved AI script, which would not work together with Proportions.

So, the general rule is that mods cannot be used together, though this is not always true, and you can always try to bend several mods if you have a bit of spare time. In the case of Proportions+TDM, the AI Campaign would probably fit the bill quite nicely, as it resembles Proportions with a tougher AI.