Blimey, I'm new here but I've been keeping sheep quite a while and you're not asking much are you? Do you have Tim Tyne's book?
Some of the answers depend on what land you're on and the veterinary history of the animals. But worming is a complicated subject with 5 different classes of wormer and a lot of drug resistance in the population.
I'd suggest you make friends with a vet - they generally offer free advice - and search some of the recent threads. There's always a lot of discussion about medication.