WeWire2:
You can get a surprising amount of backup power from a typical 5KW generator. As always, you just have to be careful with load management. Mine covers my stove, water pump, ejector pump, sump pump, frezer, two refrigerators and just about all lighting/small appliance circuits. Granted, we can't fix Thanksgiving dinner and have all of the lights on at once, but it has never let me down. We also can't run the heat, water heater, washer/dryer or A/C at all, but beggars can't be choosers.
During one particularly long and frigid outage, we used a 1,500 watt portable heater in one room and spent most of our time in there. We did just fine.
I'm using a MTS on mine that is rated at 60 amps which feeds a 100 amp sub panel. If the load use gets carried away, I'll just turn off some of the branch breakers to prioritize the available power. In your situation with only four circuits, you should be just fine with even a 3.5KW generator. I'd be inclined to pick up a couple more circuits while I'm at it if I were you.
One thing that I've found to be valuable is to include the lighting circuit that serves the area of the panel(s) so that you can see what you are doing. I've also found that an emergency light set in this area helps to get things going without fumbling for flashlights.
