You only need to worm them if there are eggs in their poo- which you find on a faecal egg count. Don’t listen to farmers who religiously worm their lambs every 6 weeks- they most likely have wormer resistance.
Most of those questions the farmer will answer- vaccines etc. But make sure you get healthy lambs, that have had adequate colostrum, look healthy and happy. Your vet can answer most of the other questions regarding flock health, and how to look after them in terms of doing faecal egg counts, when to vaccinate (and they can show you how to do it as well).