So I have been giving backup vocals a shot and I feel like I do pretty well for what it's worth. I find that I also keep time a little better. Are there any general tips, being that I'm pretty much brand new to any kind of singing while playing? Distance from the mic? Volume? EQ?
Lots of practice, distance from the mic varies, but try not to get more than about 6 inches away most of the time. Volume should be slightly below lead vocal volume. EQ varies from one person to the next.

Here's a sample, recorded with the band I'm with now about 2 years ago. First time we had played together in about 15 years, no practice and I didn't warm up enough. You can hear a few places my voice is giving me trouble and one sour note in the first chorus. Shane and I have had a running but good natured argument going, I think I hit the sour note, he thinks he did. We decided to keep it against my better judgement, about 5 hours into the recording and that was the best track so far...should have redone it again though. Total was almost 8 hours making this one.

I did all the lead vocals and harmonies on the verses, we all did two takes of the choruses to get the choir effect. I did some of the high harmonies, Alan did some of them. I did two different parts in the choruses and I think Alan did too so we wound up with 5 parts I think it was.

This ain't great, but it gives you an idea what kind of balance you're looking for between lead and backup vocals, all 3 of us have different EQ. I'm having trouble with the high notes these days, I caught the flu and kept singing right up till new year's eve 20 years ago and had no voice at all, I think it scarred my vocal chords and I lost about 4 notes off the top of my range, which is why I have a hard time with the high notes now, and on that day I didn't take long enough to warm up. Never sing with a cold or flu...We did one practice run with just one acoustic and started recording.


Anyway this is the kind of balance you would want to go for, harmony parts just slightly behind the lead. This was done with a condenser mic, different from the usual stage mic, you generally get a little further away, a foot or so... I'm the bearded guy...
Hmmm...I wonder what this button does...