Thanks for getting back to my questions, that's very appreciated. Your answers were absolutely helpful for me!No need for oil, but it won't cause harm either.
You can use a washer as much or as little as you'd like. There's no harm either way.
OC is marginally more efficient. We've abandoned our aggressiveness rating and replaced it with a better system on the new upcoming website. This outlines the differences between OC and SB more clearly. I know that doesn't help now, but I thought I'd mention it.