I didn't notice where you specify how much experience that you have working on equipment so this may be elementary and totally unessesary, but the intentions are well ment so I'll mention them anyway. Make sure that you watch your grounding. Grounding back thru somebodies electrical system, bearings or gearbox not only can get into your pocket, but probably won't help the ole reputation, especially starting out.
Make sure you carry adaquate fire extinguishers and tools on the portable rig also it wouldn't hurt to have a fire blanket or two to deflect sparks on hand either. While reading this thread, I remembered an instance where somebody local was doing some work on a haybailer around here and it caught fire before they noticed it. Tractor, bailer and a good portion of pasture went up in smoke. Oil, gas and grass might be good for getting rides; but, can get out of control in a hurry when mixed with fire. Wood chips and saw dust, can be just as bad, grain dust can be explosive.
Know exactly what has/ is in any tanks and how it will react when you fire up or breath the contents or smoke that you might encounter to work on, some things go boom or are terribly toxic. There may also be a difference between solid, liquid and gas forms. Don't use a tourch and especially be looking over the top of any barrels that somebody may just drag up wanting you to cut, unless you are absolutely sure of the previous contents or taken the apropriate measures to render it safe. Chances are nobody will check for you beforehand.
Anyway with that happy note, good luck.
Also it might not hurt to carry tags and a paddlock to lock out any breaker boxes of moving or electrical equipment, especially if the work area is not easily seen from the breakers or switches. It might be a little late to try next time.