I like the ideas of this guy: YouTube - Boxing stance training tutorial
90% of the time put your left foot in front of your head(for right handed boxers). I don't care that much about this triangel he shows but foot placement is critical.
When you see beginners who put their head in front of their lead foot in order to have some extra reach( in the beginners opinion) ,they lack balance, mobility and they expose their head through making it easier for you to reach it(less distance for you jab to travel).
You'll normally see this in combination with way too much tension in the arms and upper body.
I've read a couple of posts and i wanna stress out that everyone indeed does it (sometimes slightly) different, i think Anna said that.
When i box i keep em 60 -40 (weight, backleg front) a lot of people think i have weird footwork but it works for me.
In my case, im tall, so my game is to send a barrage of jabs.
Even when kickboxing i guess im boxing 80% 20% kicks.
Biggest eyeopener for me was when i learned from an english boxtrainer: not every punch you throw has to be full on.
As you said you want to move on eventually to mma and such, then like others already said keep the weight pretty much even otherwise you're always just a second too late for a sprawl.