My system is piped very similar to your most recent diagram, Beeper. The only differences are the supply from the OB going back to the WB happens before the expansion tank, and the loop from the OB to the zones is done with a single circ on the return side, along with zone valves. Also, I have a Superstor for DHW instead of a coil. The hydronics gurus hopefully can give you good feedback on your current design. Also, just checking to make sure you're aware of the need for a near loop for boiler return protection - is it just not in the diagram to simplify things? And, you'll also want to include overheat/power out specs in a final design.
I've got my OB turned down to 140/160. I don't have a control to keep the OB off while the WB is on, but the low OB setting effectively keeps it always shut down. The sound of the OB coming on hurts my ears, so I'm militant about keeping the WB fired. However, my WB is in the basement, which makes monitoring very easy. This type of procedural control might be more difficult with your boiler outside at some distance from the house. It might be something you could consider short-term, and then retrofit a control in later. I fully agree that you want to have a solid design that you are comfortable with before you start anything. Redos usually translate into $ down the drain. There are a bunch of threads on underground piping - try to read as much as you can before dropping anything into the trench. Good luck!