Welcome!
That transmission swap is a great first mod. And taller gearing + better aero is a good combination.
FYI, I have yet to see an example of any car where reducing cruising speed in a given gear doesn't save fuel. From 49 hp Metros to 500 hp Vettes, see:
Speed vs. mileage/fuel economy chart - Mirage 1.2L 5-spd
Another suggestion: get a digital fuel economy display. You'll need an MPGuino for your car's age (pre-OBD-II). Worth its weight in gold for the impact it has on helping you fine tune your driving technique and play the "beat my best score" game on your regular commute.