Today, I bought some linear bearings (against Spacexula's recommendation). I got the 12 el-cheapo LM8UU bearings on ebay for $18 because I figured they might work better than brass bushings. If they don't, $18 isn't a huge loss. I heard there are some small issues with the cheap bearings, but I think I'll be fine.
While I wait for the bearings to arrive, I will be cutting the threaded rods down to size and I'll begin assembling the machine.