Welcome the fun Shon! Based on your intro, you are going to enjoy every minute of ecomodding
There are quite a few option with instrumentation: ScanGauge2, UltraGauge, Torque. Find one that best suits your needs and budget. I picked up my SG2 for $70 last year, lightly used and in perfect condition.
As far as saving money, this last year has saved me close to $800 in fuel cost. That's going from 35 mpg to 46-47 mpg over the course of 23,000 miles. Getting to 60 mpg will save you around 20% on fuel cost, and that should not be all too difficult with the diesel if driven correctly.
Starting out with a partial grill block and an air dam is low mess and shows the biggest gains for the buck. We usually use coroplast (Election signs) and lawn edging for them respectively, in order to keep cost minimal and payback quick
