Every generator will have two capacity ratings. One is for continuous watts and this shows what the generator can output on an extended basis and is the more important of he two by far. The other rating is how much power it can put out for a few seconds when it starts up.
Stock up on oil and filters
Pumping out all those watts can be hard on the engine oil and it needs to be changed regularly so you'll need to stock up on oil and filters if you want it to last through a long power outage. Most new generators will need their first oil change after about one day after that you'll need to change about every fife or so hours.
Its a good idea to wear a headlight when refilling the tank so you can see what you're doing a lot easier and fill it to the brim. Make sure the engine has cooled before you pour anything. The tank is normally on top of the engine so the fuel can be gravity fed and if the engine is hot and you spill any while holding a canister of it there's a chance you will go up in flames which isn't good for anybody.
Don't let it completely run out
Some generators can get damaged generator coils if you let it run on empty as the electrical load from your house drains the magnetic field. It will seem to run fine but wont generate power and you'll have to take I to a repair shop to reenergised.