Another
I think I will forget this project and I’ll start a new one
I’ve never found adding sounds just to to “fill up space” an effective method. I would try running all my synths to a bus with a tape simulations/saturation plug in with “noise” option on it first.
Depends on what type of drop you try to make. And it depends on your tastes in music too, I guess 
True. And I don’t really do music with “drops” so I suppose take my advice with a grain of salt?
Which plugin do you prefer for that?
U-he Satin
the more time you put into a creative endeavor, the closer you get to achieving your initial vision
Might be a little more full, but it’s still weighted towards the subs and highs [to my ears].
And the whole ‘filling up space’ thing as a remedy for mixes lacking frequency balance is super… well, won’t say wrong but it’s like saying, “Here, try this dish: it’s a little bland and salty? OK… let’s add a pound of sugar, a bottle of hot sauce, and a liberal helping of vinegar. Is it good now?”
A better approach might be to pull back on all the elements and gradually, judiciously increase the attention to detail (namely presence and balance) in the affected area.
Please note: this is advice from someone who still hates his goddamn mixdowns, so buyer beware.
hahaha the thing is that we all know the theory and what we have to do, but when it comes to putting it into practice , we fail 
You don’t have to do anything.