I would like to know how much current can flow though it before it gets hot and breaks.
In essence I would like to to be able to identify how much current it takes to turn on a transistor
Gains are typical and they vary between transistors. If your electromagnet doesn't have a current limit to 1A, you will be trying to put more current through the transistor. Measure the current connected straight to the 12V supply to confirm the current drain.
It depends on the gain or Hfe. This changes with the collector / emitter current.So in order to answer your question you need to know what you want to switch. If the current is half an amp you will see from the data sheet the Hfe is 40. So you need to put one fortieth of half an amp to turn the transistor on. Which is 12.5mA.
As mentioned before this base voltage rating is a reverse voltage rating when the emitter is higher than the base...