1. The bolt guide o-rings are the same size as stock but are made of urethane. They'll end up wearing a lot slower than the stock buna ones will. I run them on my Empire markers.
2. I believe it only comes with the extra fragile paint o-ring. It wouldn't hurt to order extras especially since you'll only be ordering once.
3. If you get the bolt guide o-rings too, I'd use the brasso method to break them in. Other than that, the bolt comes with tuning instructions based on which spring you decide to use.
Any other tuning questions, check HERE.
-remove bolt guide and bolt from marker
-install new o-rings on bolt guide
-dab some Brasso metal polish near the new o-rings
-replace bolt on guide and work the bolt up and down with twisting motion for a few minutes
-remove new o-rings, wash o-rings and bolt guide with water and reassemble
This basically breaks the o-rings in within a few minutes rather then shooting several cases through it.