Put it on paper first, then have a sit down with your TAPs and go over what you have planned and then they can comment on any changes needed. Once they sign off on your design then the build process begins.
I'd suggest contacting a TAP member before setting your heart on a particular rocket. They may suggest alternate plans depending upon your experience level, their experiences, budget, the local flying field, and any number of things. Your mileage may vary. Good luck with the project and try to have fun!
Looks like a great plan to me. Good luck. I'm sure your TAP's of choice will have no problem approving that one.
Note: Most L3 failures happen due to deployment failures. Make sure your attachments points are rock solid. I would use a deployment bag system I have had 100% success when using D-Bags. Giant Leap as a nice bag setup for there TAC9 line of chutes.
A friend of mine got his level 3 on a Nuclear Sledgehammer. That is a very cool looking rocket. He had hoped to use this rocket - big and heavy - to be able to fly some larger motors at our home HP launch site. However, he made the triple av-bay as shown in the kit. It is a PITA to prep. Since it takes so long to prep, he rarely flies it. If he flies that rocket, he limits what else he plans to fly at a given launch.
He painted his with House of Kolor large metallic paint (almost fine) - red and gold. The thing glitters in the sun and looked awesome when he flew it on a smaller skid (L1400). It does a very slow but true liftoff on that motor.
Make sure you have friends with strong backs. That is a heavy thing.
The lengthened Nuclear Sledge Hammer is definitely a very stable and proven design. GLR makes very nice kits.