For your Inverter and generators you need to plan your electrical usage and all the loads.
Many of your electrical appliances, heaters, TV's and so on have a measurable amp. draw, or the amount of electricity they use. They will have tags that state that information.
Smaller loads, clocks, small fans, radios, things with a cord to plug in may not, or you have to do the watt/amp calculations if they do.
In the trades we often use what is called a load multiplier, or a dozen other names across the country.
I will show you how to make one yourself.
You will need an amp meter, jaws that clip on a wire. Sears has a great one that measures 12 volt power with it's leads,(you can check a battery, by touching the posts with the leads) and measures 12 volt amp. loads with it's little Jaws.
You will have to have a tiny bit of handy-man knowledge for this, but not too much. It takes about 3.5 feet of wire to coil into a small circle, but coil it 10 times for the multiplier. Just wire in a male and female plug you can get at the hardware store. Wire nuts or butt-splices for the coiled wire, or wire it into the plug.
I have a picture here. You will be working with small loads, so you don't need a heavy wire. (everything that draws 5 or 6 amps or more will have the nameplate with it's power information on it.) The smaller loads probably have it too.
Hope this helps.
Amprobe
This is a way to accurately measure the amp draw from small loads. Take a wire and wrap it 10 times, take a reading on a 2/10th amp load, it reads 2.0 amps on your amp meter. Obviously you need to wire in the end caps.
This is about a 16 ga. wire, the big red cord is a 12 ga. wire.