Ok, first off, starting to come togeather, way to stick with it and finally get a good start on it.
Second, Zach, put some sort of bumper re-bar in there, even if its just some pipes. If you hit anything, or even get an empty cardboard box tossed up at hiway speeds your I/C is toast. You can buy aluminum bumper rebars that are made to fit nicely and bolt up to the stock car in the stock locations. They are small and very light.
3rd, that ABS g load sensor can be bolted down to those two holes just up and back of where its sitting, dead center. It needs to be held steady to work well, and ABS is a good thing to have.
As for dash, I don't think I would be taking out the dash, thats alot of work plus alot of custom shit so that you can have a working heater and defrost, and gauges, dash, lights, ECU etc. And even on a track car, a heater and defrost are a good idea. I know you don't NEED them, but some evenings, when it cools down, you get a steamed up windshield. Roof and windows must be closed to run. And if you plan on doing any rally, autox or road course/hill climb events, you will want a working heater and defrost.
As for the weight reduction, I would estimate that at 200 lbs. I took all of my rear(behind the front seats there is NOTHING) interior out and I gained 163 lbs. I weighed each category of parts(bag of screws, bag of brackets, seats etc) The seat back setup is very heavy and the rest all adds up quick. Now, 100 lbs is 1/10th in the 1/4 for free. So 2 hunny is helpful to say the least. And its the gift that keeps on giving. No matter how much power you make, your car will be faster with less weight. It also helps with cornering and braking, fuel economy and, well, top speed too if you were power limited. That said, unless your car is a track/weekend toy, keep it nice inside.
Of course this ONLY is good for a weekend toy/track car. It sucks hairy goat balls as a commuter. LOUD as HELL!!