I would build it over the plans like they say, mark the firewall on fuse side from the plans, and mount the wing, then mount the tail last and eyeball it so it is level with the wing side to side. The kit is built in a way that all the thinking is done for you. Mount everything where it is on the plans and you don't have to worry about that stuff. You can double check it, but thousands of those kits have been built just by putting it together, and they all fly. Don't over think it.