What exactly are your goals for this system? Is this going to be a demonstration vehicle for the store? Are you going to compete? Do you have a certain level of loudness you prefer to listen to? I've found it doesn't take much money invested into equipment to be able to get a really good sounding 1-seat car at 90 dB, which seems to be no louder than vehicles are judged for in SQ competition.
Without going line-by-line over your proposed equipment list, you could probably slash than by 50% and still have some incredible potential. What you do with that equipment and the vehicle is more important. This is why keep_hope_alive keeps talking about hundreds of hours spent on the vehicle, yet he doesn't use thousand dollar speaker sets. If you want expensive speakers to show people what Audison has to offer, then go for it. As a side benefit, you'll have better results getting your money back if you ever decide to sell the equipment than if you bought run-of-the-mill products.