Lots of good advice here. Most onroad and 1/8 scale buggies will use metric wrenches. It sounds like you are getting pretty serious, and in that case, I would recommend going with quality. I have used many different brands including Dynamite, AE, Integy, RD Logics, Protek, Serpent and Hudy. The Hudy are hands down the best. I round off less bolts and they just fit better then anything else. The Serpent tools are right there as well, but they are not as readily available.

Airbrush is good, reamer is pretty much a necessity. Good lexan body scissors a must, and for onroad, a circle cutter is very handy.

Drill no, dremel is handy though. Screwdriver is also handy with 1/8th scale.

Consumables will vary but there are some staples. Double sided tape (I personally perfer the clear silicone as it leaves no residue), solder, battery tape (strapping tape, you will need this if you go onroad), heatshrink, 12ga wire (deans wet noodle is my preference, 12ga will work on most 10th and 1/8th scale), connectors of choice (deans and bullets are what I use). You will also need fluids for whatever you are working with. Shock/diff oils, bearing grease, CV grease, etc. Locktite will be a must with the 1/8th scale, red and blue. You will probably need tire traction compound of some sort for onroad.

Tuning tools will vary based on what you are running and I would tend to hold off as you will need different tools depending upon onroad or offroad. For what you have now, picking up a cheap offroad ride height gauge and camber gauge would be useful. Tuning in offroad and the exactness of it is much less then onroad. While eye-balling is not quite good enough, a full setup station may not be required either. In onroad, being off half a degree of camber or toe can make a car nearly undriveable.

Good luck!