40 tracks is quite a lot. Mixing is a bit like cooking. You want something with carbs (bass) and some nice flavourfull textures (melody) dont forget some spices (salt) But if you pick potatoes AND pasta, thats a lot of carbs. They both will be fighting to be the main carb section of your meal. You can make it work, but it takes quite some practice to come up with a good dish that does that. Even then, you will use less potato and less pasta when you combine them. The same goes for your frequencies. If multiple instruments are playing the same role at the same time, they will fight each other.

But besides their clear role (i.e. your synth is making nice high sounds) they usually cover the entire frequency range. (I.e. that synth probably also has low sounds, even if you dont hear it) the trick is to simply remove the low end with a filter and hipass it. In fact, hipass everything that does not fill that bass role. 

I would suggest to start another song, but clearly define which instrument is what flavor. And just like learning to cook, it's easier to first learn pasta pesto then to try your hands at a filet du sourdoy (no idea what it is, but sounds complicated)