Amps times voltage equals watts. 5000 watts divided by 240V equals 20.8 amps. A 2HP pulls a max of 13.2 amps. It is the start up amps of about 70 that is hard on the generator. But that size generator should have a peak starting amps large enough to handle it. Pumping the well at low pressure and max flow will usually help pump out the sand, but you may need to pump for hours or days.
Now that you have a pump large enough to supply 18 GPM to the largest zone, how are you going to handle the smaller zones like the drip? If using a pressure tank and pressure switch, that pump will cycle on/off when using any less than 18 GPM. If just running direct to the irrigation, the pressure will be really high when running the small zones.
A Cycle Stop Valve with the pressure tank/pressure switch will solve the cycling problem and you can run zones down to as little as 2 GPM. Plus the CSV will greatly decrease the number of cycles and the duration of the inrush amps on start up.
A Cycle Stop Valve by itself will let you run the irrigation direct, with no pressure tank/switch, and would maintain a set pressure for the smaller zones all the way down to 2 GPM. This way the small zones would not have way too much pressure.