Hey Steve,
Kudos on a good gig ...well done, man!
1. OK, so feedback issue is solved, it seems? As you've already read, proximity is key and particularly in close confines, playing/singing
behind the plane of the speakers solves many a malady.
2. I have long since learned to never, ever, ever make volume or tonal adjustments based on what I hear on stage: it's
all about what the
house hears. Yes, I get it, we as players/singers want to hear what we want, and this makes sense, particularly to stay on pitch and in tempo; it's a potential disaster if a performer can't hear what we need to hear. But we learn to sacrifice our wants and accept less-than-ideal sound
on stage so long as the house gets the right balance and tone. Your friends gauging your tone and balance in the back of the house are right on; the
audience listener is your barometer. You're fortunate to have your buddies there as that's seldom the case, as more often than not we gotta trust what we "think" is right ...go buy em a drink the next gig (and tip your bartender)!

3. You may want to consider a small monitor so you can adjust for your personal mix. It will add to your setup/teardown time, and potentially complicate your sound check (which is scarce time as it is) so if you can learn to make due without one you're good, but a monitor done right is a wonderful thing.
4. General rule for vocal/guitar balance: 99.97264% of the time, your audience cares little-to-nothing about guitar volume or tone, so long as it is present. The songs are about the singer. Period. Ask any regular Joe who is
not a player: they're "hearing" the band but
listening to the singer.
5. You rocked and the audience dug it: that's all that matters in the end ...congrats!

Edward