As a vet, often the cut off is 300epg, but can somewhat go on signs too, if 500 but no scours, everyone is growing well and not thin, could consider not worming.
If you do worm, using white wormed is a good idea, it is cheap and generally safe, but do as said above, weigh goats accurately because they are heavier than they look, even to vets! And do use double the sheep dose.
Checking at 10-14 days is a great plan to see if you have any resistance.
PLEASE do not change workers every year, this is now known to increase the chances of getting resistance.
It is also worth having them on pasture that has been used for grazing for a week or so afterwards, that way if there are any resistant worms left in the gut, they will have to fight against non resistant worms that get picked up from the dirty pasture.
Have a look at SCOPS, although its for sheep, it can be applied to goats as well.
Hope that helps
Suzanne