Your new sheep will have been tagged on their holding of birth. If they are tagless do not accept them. They will keep those tags for life.
You only need your own tags once your sheep lamb on your holding, so the lambs are tagged with your information. You do not replace the tags in your bought-in sheep.
We rarely buy in sheep now as we run a nearly closed flock. However, when we do, we get wormer and flukicide doses from the vet specifically for those animals. If you can get Zolvix then you know you will be starting with clean sheep on your clean pasture. Treat the sheep in a pen or shed on hard standing, leave them there for 24 hours, then remove any manure and bedding and burn it, along with any shed worms. Thereafter, you need only worm them if they look seedy, and then only the individuals which are off colour. Until you have learned how to recognise a wormy sheep, take a FEC (Faecal Egg Count) sample to your vet to see if your animals do have worms or if it's something else. Your vet, who will know the area, and may even know your land, will advise which wormer to use. For fluke, it depends on your land, and the land your new sheep have come from. We are lucky not to have fluke here so we do not need to treat other than on arrival, but again your vet will advise. Current thinking is very much against routine worming, although you will still get this advice from neighbours sometimes. Routine worming leads to wormer resistence - ie the worms are resistant to the wormers.
Depending on when you get your sheep, you will need to use a flystrike preventative in the 'fly' months - again discuss this with your vet. There are various products to choose from depending on your numbers and needs.
Spend time watching your new animals. Lean on a gate and observe what is their normal behaviour. This will allow you to learn when there is something wrong with a sheep, which will act a bit off, and may need vet treatment