I like the use of the word "ash" in common762's post. Never heard it called that, but technically he's right. An excellent term for discribing EDM to those who no nothing about it.
The electrode material choice for busting taps would be copper-tungsten rod. Cheap enough and you can get it in all kinds of diameters so you won't need to fabricate anything.
I'm not familiar with that machine, but odds are you will be using a water based coolant. Actually, that is a total guess just going off of the "portable" adjective from your post. Just can't picture oil base Ram's as portable... I use Red Line synthetic hole popping fliud. I get it from Electrodes. I'm sure they would be more than happy to point you to exactly what you need.
I would add this also, if your spindle doesn't rotate... not index... rotate..., I would see if you can get a retro-fit to make it do so. Makes "blowing through" stuff a lot faster.
Good luck and welcome to EDM noob... You'll get hooked I'm sure..