Bringing on new animals is the one time I would always worm them all, preferably before they go into the trailer so they will drop any worms before they reach my pasture. Ask the seller what their worming regime has been and what product he has used. When I am selling sheep I worm them as they are loaded so the new owner starts with clean sheep. Once you have got them home, particularly if you have not had sheep on your ground for years, it is unlikely that you will need to worm them again, or maybe just once, a few weeks before they go for slaughter (if that's where they are headed). Moredun, the Animal Husbandry Research place, recommends that sheep are wormed only when they need it. So either you get a worm count done every now and then, or you learn to recognise in your animals when they look 'wormy' so can dose that individual animal. There is always the small risk that you have bought in animals which carry a burden of wormer-resistant worms, which would be identified from a worm count, so if they fail to thrive over the next few months you would suspect that and seek veterinary help. Check too whether the seller has a fluke problem on his land, and when the lambs were last treated with a flukicide. If your land has standing water then you are likely to have fluke so should seek vet advice and treat them in about October.
Injectables such as Dectomax will worm (some types of worm) and also prevent scab, which is on the increase since compulsory OP dipping was discontinued.
The spray/pour on is to prevent fly strike. Again check with the seller when they were last treated and if they will need to be done again this year - we are nearly at the end of the fly season, although not quite.