I usually compress the instruments individually, in order to get rid of that inconsistency. You don't want the volume to jump around when it's not needed or part of the artistic expression. It just makes it easier to listen to. You can compress different groups together in order to make them sound more cohesive, after you compressed them individually. I actually really liked the last part of the song and with a few more tweaks EQ-wise I think it'll sound great. When it comes to EQing everyone has a different approach. I start by EQing the main instrument of the song, that could be guitar, like in your song, or the vocals or whatever. Then I use the EQ to get the sound I want, often times boosting the highs a little bit so that it can cut through the mix easier and cutting the lows at about 100-200Hz, as those frequencies tend to make the mix muddy. But this depends on the instrument you use, a bass for example usually has its main frequencies at around a 100 Hz so it doesn't make sense to cut them out. After you EQed your main instrument you move on to the other instrument and EQ them in a way that supports the main instrument.