Welcome to EM.
The Matrix is a great car. I have a 2003 that I am just getting ready to sell. With some mild modifications and driving techniques I was able to get 47 mpg out of it, and 40 pretty consistently with me and my wife driving. 45 will not be a walk in the park, but if you use P&G you should be able to get there.
Here is my build thread:
http://ecomodder.com/forum/showthrea...read-1890.html
BTW, your mods list looks good, but the prices are a bit off. I'd say way more then $200 for tires, and waaaay less for a belly pan.
Good luck, it looks like you're off to a good start.
