I need to order baseboards and am wondering how to go about measuring for them. Some things I'm wondering about are whether to disregard door casings or other trim that's in place or to subtract them from the floor plan dimensions? How do you account for the amount extra needed for mitered corners? Doesn't that add about an inch per corner for a 1/2" thick baseboard? How much extra do you include for waste or errors? Do you make a list of cuts and figure that way? What's the best way to assemble the cuts into board lengths? I'll be getting 16 foot boards. Anything else to consider when measuring and ordering?