Well, the backyard concert was a definite success!!! I'll be doing it again next summer!!!

We thought for sure we would have at least a little rain, but we didn't get a single drop. Since the forecast called for rain, we had set up a tarp running from the roof of my house to two ten foot poles dug into the ground and some ropes (my friends took care of that). We didn't end up needing the tarp for rain protection, but I think it did help keep the noise within the backyard. Some wicker torches (about 8 of them) spread out around the backyard added a cool touch when evening fell.

For sound equipment, I rented a 2x250W amplifier and two 200W speakers on stands for the vocals, piano and acoustic guitar. I also rented a Shure SM58 mic which turned out to be pretty good for vocals, and a Takamine electric/acoustic guitar.

There's a little patio that adjoins the back of my house, so we set up shop on that, and the audience sat on some more tarps which were spread out on the grass. We put the speakers on either side of the patio (about 20 feet apart). The balance of the sound was apparently pretty good, according to some comments from the audience.

We did only covers and the show lasted for about an hour and a half. Our best songs were probably a song called "After the Rain" by Blue Rodeo (2-minute outro guitar solo!!!) and a cool "Moonlight Sonata" instrumental that everyone loved, in which basically everyone went crazy on their respective instruments (imagine a quiet piano intro, fade in drums, then bass, then a clean lead guitar starting muffled on the neck pickup, switch to bridge, then kick on the old MT-2 and 535Q wah-wah and keep going 'till you can't tap no more).

Thanks again for all your suggestions and advice, guys!