Adam:
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Would it make sense to just put more parts in the bath to increase the load and get a reading I can actually work with?
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Simple answer: No.
Contrary to what common sense would seem to tell you, adding more parts (increasing the total surface area) actually DECREASES the effective resistance of the electrolyte cell.
The electrolytic cell is a strange beast, it does not behave like a either a fixed or variable resistor.
However, larger parts will need higher voltages, so it may work anyway, particularly if your PS is designed a voltage source, and has a lower limit. You'd have to try it and see.
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I assume I'll need a 1ohm resistor that can support the maximum amperage the unit supports?
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It doesn't HAVE to be 1 ohm, but 1 ohm is a very handy value, since voltage across 1 ohm is exactly the same as current through it. Using any other value resistor, you'd have to do a bit of math to calculate the current.
eg, with a 2 ohm resistor, if you're measuring 5 volts across it, then current would be 5÷2, or 2.5 amps. 1 ohm eliminates the need to do math.
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In this case, we're talking about a 25 amp continuous unit with a peak output of 30amps.
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You'll only need a resistor big enough to handle the highest voltage & current that you expect to ever need.
You haven't said how big your tank is, or how large your anodes are, and you will be limited by those.
25 amps is enough for 180 sq-in. at 140 ma/sq-in. Are your anodes that big? Do you forsee doing parts that big? Even with parts that large, your voltage will likely not exceed 6 volts.
The largest piece I've done was @120-125", at 80 ma/sq-in., and it came in @ 2.5 v. Using 140 ma/sq-in would still have been less than 5 volts.
So if you want to assume 6v, 25 A as most you'll use, you'd need a resistor rated at 150 watts (6x25). That's a fairly good size resistor. If you want "worst case" for anything you might throw at the PS, then 15v x 30A = 450 watts! That's a HUMONGOUS resistor!
You can get a 10 watt, 1 ohm resistor at radio shack ($1.80). That would be enough to plate at 3 amps for now, and to test your PS meters functioning.
Anything bigger than that you'd need to go to an electronics catalog house.
Sean