good advice so far by the group. transfer panel is a necessity.
When adding up the volts x amps from each device, keep in mind that motors(such as are on well pumps) are a special case. the starting current can peak to 3 times the running current since when the starting windings cut in the motor is not developing a lot of back emf to limit the current. My water pump motor at the bottom of the well takes 9 amps running and thus 27 amps starting. Same for the pressure pump. Thus 54 amps x 220v would be the worst case if both could start simultaneously. To save a bit here, one could fill the storage tank, cut out the breaker, and use the pressure pump only till the tank is low, but make darn sure your pressure switch has a low pressure cutoff which disables the pressure pump motor below a minimum amount(most are 20psi). That is necessary to avoid running the pump dry which will kill the seals very very quickly. This is cheap insurance as it costs about 5 bucks more for that pressure switch vice the ones which just turn off at an upper limit and will start even at 0psi.
the 220v non motor items require the current to be multiplied by 220 when sizing them
if the generator is in a remote shed away from the main house I needed a way to find out when the utility power has been restored. I put a small floodlight on the utility side of the transfer switch and switched it on when I pulled the transfer switch after starting the generator. If you can see the shed from the house, and the light is on, you know you can switch back to the grid.
I think diesel is the way to go for larger setups of 10kw or higher. You can get fuel stabilizers for the diesel too. The backup generator should be run for a short while every week or so.