Really good tips in here! Is the track being released somewhere? Really digging it!
However, I think the Hi pass filter tip is really quite dangerous. I did apply it quite liberally before, but then when playing around with bass sounds, I noticed that high pass filtering really alters the sound of the bass. And if your bass is playing more than one note in the scale, this can be a major problem as the tonal quality of the bass can be shifting per note pitch. The effect is even more pronounced if you have some non-linear processing later in the chain (like distortion).
This all comes down to phase shift, which all filters do. So applying high pass filter on master track just to be on the safe side is something I really would not do anymore.
Also, when filtering tracks that have same phase content (synth and reverb/delay send) you can easily introduce phase alignment problems. There are some good youtube videos explaining the phenomenon (White Sea Studio and Owen Palmer for instance)
So just be wary of this and don't hi pass filter just because you think it's something you should do. Always do it in context!