[Otaku]

I'm assuming that the circuit breaker is a 15A, so yes, you'll be popping it with three foggers and a few lights. I have a similar problem - only two outlets in proximity to the display.
It seems odd that a GFCI would trip on an current demand overload. They're designed to trip on ground faults - inconsistencies in the ground line vs. the "hot" line, such as what happens when you drop the toaster in the bathtub. The actual circuit breaker is supposed to trip when the current demand exceeds it's rating. Are you certain that one of your lights doesn't have a short somewhere in the wiring? The inrush current demand from a fogger when the heater turns on can also cause spiking problems.
You may want to invest $20-$30 in a Kill-A-Watt meter so you can check the wattage draw of your devices. Changing over to LED spot/flood lights will reduce the demand, as well. You can also try using battery-powered LED spots for individual prop lighting.

 

[Otaku]

The two outlets that I use for the display are on individual GFCI outlets. In fact, all the GFCI's in my house are at the actual point of use - none are at the breaker box. I've never seen multiple outlets ganged to a single interrupter. It may be moot, but it seems a shame to kill power to non-faulting outlets.
Perhaps you could have an electrician remove the multi-GFCI from the circuit and replace the outlets with individual GFCI's, but I don't know if that would gain you anything since you would still have three outlets going to a single breaker. The alternative is to cut in new breakers, of course.

 

[Otaku]

I may look at the LED option a little bit. A lot of you seem to have reported success with them, so I'll do some more reading.

For individual prop lighting I use small LED spotlights that I make myself. They use anywhere from 3-5 ultrabrights per spot, and run on 9 volt batteries. There's a number of how-to's on making these. I really like the portability and that they don't need any AC cords. The batteries have lasted for two seasons with no noticeable dimming (~ 40 hrs).