I am thinking of installing a 1 HP water pump to water my lawn. How many
sprinklers can it support? Is there a rule of thumb or some math to
calculate?

What would happen if I don't install enough spirnklers? I worry the
pressure in the pipe system would be high and ruin the pump.

The sprinkler is this type:

https://upload.wikimedia.org/wikiped...echanism_2.jpg