If you only intend too keep these sheep (or any wethers - excellent choice to start with, but I would choose a traditional breed, like CMM or Shetlands, that won't put down too much fat in their second summer) for a few months it isn't worth your while to vaccinate - but you can insist to buy vaccinated sheep. Clostridial disease is not brought onto the land by incoming sheep - but worms, fluke, footrot and some other things (can't just stretch my brain any more, just been mucking out goat pens) are.
I would also not buy any sheep unseen, I would be a bit suspicious if someone is really keen to get rid of them... and even deliver them! You want to see how they walk (foot problems are endemic this winter due to the wet ground), and put your hand over their spine to see how skinny (or not) they are atm... Also remember they will need clipping in early summer.