Your plumbing choices may be affected by how many holes are in your overflow. If you have 2, I would suggest a herbie. Has worked well for me. The only part you may not have readily available is a gate valve, but that shouldn't be too big a deal to get ahold of.
I agree with the no eggcrate beneath your rock. Your plans look great, I'm sure you're excited with a fresh start to your aquascape. Keep us posted!
- Ian