I have a 7500 watt generator. It can power most of my house including all my tanks. If you're getting a generator for your tanks you might as well get one for your house. You're still going to want to eat, use the computer or watch tv, have other stuff on while your tanks are surviving the power outage.
Once you settle on the size get to know the generator. I bought mine almost 4 years ago and did nothing but run it a few times. I have survived as long as 33hrs without power. However you really should run the generator every few months or more frequently just to make sure it's running. Keep some extra gas on hand but not too much unless you are going to cycle through it since it does not last forever. The first time I used my generator I was shocked that a full tank only runs it for 11hrs. I keep enough for 24hrs on hand most of the time and if a storm is coming or just a random power failure I will go get more gas then.
Last winter, actually on new years eve my generator wouldn't start. Despite having no idea what I was doing I was able to change the spark plug, clean the oil filter ect. Better to learn how to do this stuff sooner rather then later. The generator was 3+ years old with maybe 50-75 hours of use on it before it required moderate service. Having an extra spark plug, oil and other essentials can be just as important as having enough gas. A new one should run flawlessly for a while, but not forever. They require maintenance which to some may seem obvious, but to others like me you think "I'm not worried about power failures I have a new (that is no longer new) generator in my shed, I'll be fine".
