Welcome to the starting point of getting addicted to sheep ! We've only been keeping sheep on our smallholding for a couple of years but in answer to your questions and keeping it low cost ....
1) If you're after meat lambs i would consider something with a texel or suffolk in it but if you're willing to give it longer until Jan them most breeds would be an option, we have some Derbyshire Gritstones and love them !
2) I found our most useful things were a few sheep hurdles, even just 4 to make a small pen if you need to pen any up, a bag of feed and a bucket (we have a bright orange one for feeding) to 'bucket train', getting them used to this makes things so much easier and ours just walk into a hurdle pen. If they are wormed then that won't need doing, if they are treated against flystrike that shouldn't be a problem after the next month or so but I would get some immature fluke treatment and treat in October and December if bad fluke areas and I would just get a couple of syringes for their dose rather than spending extra on a drench gun.
I would get a salt lick which are a couple of quid from our local countrywide store, a marker spray in case you need to identify any you have problems with, we have antibiotics and antibiotic spray from the vets in the cupboard which are very useful to have but we only brought them when needed and now just have them on hand. The other main thing we use the most is electric fencing which for 4 lambs you could split an acre paddock to allow some rotation but for just keeping 4 until January I woudn't bother ! but hay will be needed when the grass quality drops.
3) If your after some for sale Preloved or Sell My Livestock may be useful or local livestock sales. We are staffordshire based all of our boy lambs are sold but I have 2 female lambs left as I can't decide whether to keep or sell as they've very sweet.