Most of the questions can be answered with it depends:-
So an inverter generator is normally petrol and will vary in speed depending on the load, so it will use less fuel when on low revs, and it will also produce less noise, often the inverter input can be shared so you can use two generators in tandem, they tend to be lighter, and I have seen many used by caravans just sitting outside their caravan.
If not an inverter generator, the speed is fixed, but since the speed is fixed, diesel works quite well, they make in general more noise, heavier, better for a continuous load, but not so good with a varying load. The law changed this year, so now need to use DERV not red diesel, so the big advantage is now lost.
There are TVO generators (tractor vaporising oil, better known as 28 sec gas oil) they start on petrol then switch over, liked by people with oil fired central heating, don't know how the law change affects them?
There is also the Wispergen really more for yachts, uses a Sterling engine (external combustion) as one would expect with the name, very little running noise. There are also some units used with caravans, not sure how they work, think no moving parts, but not looked into them.
The big question is how long will they last, I would think there is an option to use a generator to charge my batteries, I have not really looked into it, if I had a power cut now, battery at 86% charged, it could last for weeks, depending on the sun, as only central heating and freezers run off the battery back up, but by 9 pm will have reached a point where it may not even last the night.
I have torches for light, and a portable gas ring for cooking, from when we used to camp, and an open grate which has a board covering it, but could be soon opened up, but living in the countryside, we have three freezers, and that would be a large loss if they defrost. The chest freezer will likely last 24 hours or more without power, but the upright freezers, all down to when the last defrost cycle ran. If it was due to run just after the power cut, then likely will last at least 18 hours, but if the defrost cycle has just completed, then food in the top has likely an hour at the most, food further down likely OK, but until power returns one has no idea what the temperature is inside the freezer. Mine will display the temperature inside when the power is returned until I open the freezer door, so at least I know if it has warmed up too much.
Opening the chest freezer lid during a power cut not too bad, but an upright no way should you open the door. But the chest freezer has a single phase motor and a large inrush on start up, the upright freezers have a three-phase motor and an inverter drive, so no massive load on start, but the defrost heater is on mine 1.2 kW, so any generator must be able to supply the start amps or the defrost heater, there is no option to disable the defrost heater.
So we need around a 3 kW generator for the freezers, but on saying that, on the Falklands the 1.5 kW diesel generator was popular, and it did run their chest freezers, no one on the Falklands would get an upright freezer. I have put energy monitors on the freezer, but not convinced it will show the peak start amps, only way is to try it. Some generators with an overload will shut themselves down, other will burn themselves out, it depends on how they are controlled, on the Falklands we found if we started the shears sharping disc first, the rotating mass of the disc would allow the shears to start with the 1.5 kW generator, but they would not start if the disc not running, it needed the 12 kVA to be started.
All well and good when you know what to do, not so good when you don't. I have considered an inverter generator, it would have been handy when doing gardening so no need for extension leads for hedge trimmer etc, but moved to battery powered garden tools instead.
