Looking forward to doing business with you
I don't think the Stillen CBE would be an issue for your power levels. Those mufflers in the back would have to be heavily baffled to be an issue when attempting to make 500whp. I also believe that the exhaust would bolt up to the OEM Y-pipe, which means you simply order the kit with the OEM down pipe, and you are set...something for you to look in to I guess.
Oil cooler would be a credit, and you no longer need your high flow converters.
Air/fuel sensor and monitoring, a vacuum/boost gauge and a pod/housing for them is a great start. Some customer opt for a few other gauges, which are nice to have but most definitely not a must.
The guys at Specialty Z are very familiar with the kit, as they have now tuned a few cars with it. They could also be a great resource for information when it comes to additional upgrades. RE11's...great tires.