David.... the first step to a better mix is realizing that you need a better mix. No one can teach you mixing.... unless you pay money and go to a school that teaches it. But that is expensive. So in the end, you must learn for yourself. All we can do is offer some advice and tell you to be patient, study hard, and mix lots of songs and have a look back in 3 years or so. You'll see you have made progress.
Now on the part about how you get it? Man... the experts have written libraries full of books on every aspect of the topic. Buy a book and read and study it so you have an understanding of the topic. Then try those things in YOUR mixes.
My advice would be to start at square one. Go back to the individual tracks.... I build a mix based on the bass and the drums as the foundation. All other things build on top of those 2.
Try to get the tracks sounding right...straight in. If you have to use FX and plugs with EQ to get a track to sound good, it probably was not recorded as good as it should have been to start with. In 90 percent of my projects, there are NO plugs in the tracks. The tracks are straight to the master buss with no EQ.
Vocals tend to be effected a bit. Mainly to bring out the sparkle. Vocals..... man, that's a topic that could easily fill several books alone. With vocals, you really need a clean recording of a singer in tune....or use something like Melodyne to tweeze the off key notes into the scale.
Since you have MC3.... I would attempt to do ALL my recording IN THE BOX. I understand the whole "crappy equipment" thing.... but you can still make clean recordings. Do not use the BOSS BR-532 for recording unless it is absolutely needed... (as a preamp for a mic or something.) I started out using a similar all in one Korg and it actually was making the tracks sound like crap. I plugged the mic straight into my interface and suddenly it was crystal clear and clean as a whistle. I sold the Korg on Ebay the next day. You didn't say what sound card or mic model you are using. A good mic and soundcard should give you quiet clean recording backgrounds with little noise or hiss.
As far as monitoring... I would not hesitate to use a decent set of headphones if that was all I had. I'd use headphones over $7 computer speakers no question at all...... use what you have until you can pick up some studio monitors. No problem.
I was mixing last night the newest tune I posted. I think everyone fights with the volume... because I was fighting to get the vocals up where they belonged in the mix on the new tune. Then it was a back to square one moment..... if the vocals won't go up.....everything else MUST COME DOWN. Plain and simple..... but so often never looked at as the answer..... most times we pop in a compressor, and some other things to boost the levels well beyond the red line. I went back through every track, checked it's assigned busses and pulled levels down and started mixing again from that lower perspective. Suddenly, everything gelled. The mix came together flawlessly in a short time at the lower level.
I use busses when I need to. I don't use busses just because I can. I might have 2 or 3 sub busses for :
1. vocals (if I have several vocal tracks),
2. guitars (again if I have several), and on occasion
3. I will place the bass and drum kit into a buss simply to control their level in the mix as a group as I did in the last mix I posted.
On good EQ: the best EQ is when you don't need to use EQ. If the track is right, no EQ is needed. I try to keep my EQ as flat as possible, and just like volume issues.... EQ works best when you CUT the offending frequency.... not boost everything else. If you are going more then 3db up or down on EQ... you probably want to consider tracking the instrument better. It's not a cardinal sin to boost something 5db if it works..... but that is not something you want to get into the habit of doing.
Some more advice: SLOW DOWN. I know that when I have a new song written, and I want to record it.... I WANT IT NOW! Done, finished, mastered, sounding good, brilliant guitar solo's, etc, etc, etc...
Sometimes getting it right takes multiple tries over several days or more. As home studio owner, you are not recording to a clock that ticks away in dollars. You have all the time needed to get it right. So... if the singer is singing off key... you can delete the track and do it again or punch in the fixes.... no time limits. Its when people get in a rush they settle for second or third best rather than working on it until they get the absolute best take on a track.
Your example kinda sounded like it was thrown together rather quickly and called "done". Back in the day, I did the same thing. If I tracked a guitar and I kinda missed a note or timing was just a slight bit off... hey no problem, it adds character. Now multiply that across 8 to 10 tracks and soon you have a real mess on your hands. I now go through every track listening for the glitches and mistakes. Nothing stays that is off even the slightest bit. I listen to vocal takes for the smallest pitch issue, or clicks and other lip noises. They all must go. I don't care if it's a country artist or a Seattle grunge band, none of them allow less than perfect tracks out of the studio.
I hope this points you in the right direction..... the song sounded good, but there is obviously some work that needs to be done. Take your time, learn a few things.... ask questions here and get those mixes up to speed.
I've been here almost 5 years now.... I have seen improvement in my own mixes, and I have seen lots of people come here and with time, their mixes have improved. I have confidence that you can learn this.