It all depends what minerals your ground is lacking in? ask your neighbouring farmer what he/she uses. Your supplier will also help you, the buckets/tubs come in 20kilos don't worry they are not to big and your sheep will soon get through them, we use a variety of brands "crystalyx" "uniblock" there is also "rockies" mineral licks.
Buy a bag of cake and feed a little to them every 2 or 3 days if you want to, but bear in mind the object of your exercise is to get them to come to you not feed them up, with good grass on its way they don't need feeding, put a trough in the field put a bit of cake in it and walk away they will soon find it, you'll find after a couple of weeks they'll be knocking you over for it, don't overfeed them and if you want you can then stop and leave it for a while, don't worry they will soon remember the rattle of the bucket or bag!! May I suggest the best dog option is the plastic one!! ie: the bucket or the bag to get them to follow you. You haven't got enough sheep to warrant a working dog, it not fair on the dog when all he wants to do is work and you only have 4 sheep!!