You're welcome!
Dealer Inspire was initially started under similar circumstances, an ad agency that was frustrated with all of the crappy website vendors. The advantage DI had was back when they started there were not a bunch of "great" website vendors, whereas you now have a much higher benchmark to overcome as there are many great website vendors, with DI being at or near the top. If you decide to still move forward, I sincerely wish you luck on your large ambitious project and hope it's a huge success.
However, since this project is easily going to take months and months to complete, I would highly recommend devoting some of your team's resources to continuing to improve their existing site so you don't leave the dealership at a standstill. Don't let the dealership give up on their current website by solely focusing on something coming way down the pipe.