I had the engine running today and took the negative battery cable off and the car died. Am I to assume the alternator is no good? I have no gauges or warning lights yet so (fuses probably) no red light to observe.
Normally removing the battery cable on a vehicle with an alternator "Fries" the alternator. Usually the diodes which are easily replaceable.
if you get a voltmeter, you can do a pretty accurate test yourself
1 - test batt voltage with the ign off, should be ~12.5v
2 - start engine, voltage should rise to high 13s, maybe 14
About cleaning the gas tank: If the vehicle it has sat for years and may be rusted though, you can expect to take it off and use any of the available "gas tank etch" cleaners, or take it in for a professional cleaning/repair. That will let you know if it is usable or salvageable. If it just has the sticky residue of dried gas and dirt, and is sitting on tires and suspension, I have had good luck draining the tank (if it is not already dry), pouring in a gallon of good carb cleaner, and alternatively rocking the vehicle and letting it sit, for a couple of days. (That trick once saved me from having to pull the tank on a VW bus, which first requires removing the engine, etc.)