Our regime is: Primitive lambs born in April; tup and wether lambs weaned at 4 months so mid to late August; ewe lambs are often left in for another month for the ewes to wean them naturally (but if the ewes were thin as you say yours are, then all lambs would be weaned at 4 months). All lambs out by 5 months, which gives the ewes a full 2 months to recover before going to the tup in November.
We allow our Primitives to breed at the natural time of year (tupping in Nov, lambing in April when the grass is growing), so we would not be putting a breeding tup in before Nov, especially with the ewes in poor condition.
You will be getting different advice from different sources because larger breeds and commercial sheep have a different regime, where lambs can go off for slaughter at as young as 3 months, straight off the mother. It is beneficial to lamb early for commercial breeds because early lambs fetch a better price. With the Primitives, which includes Shetlands, they are usually not large enough before the winter to go to the abattoir, they put on very little condition over the winter, then fatten on good spring grass and are ready for slaughter at 15 or 16 months. As it costs the same to slaughter a tiny lamb as a larger one, and if you have enough grass or can rent land to fatten them, then you will get a much better return for the older lamb. Lamb meat at 16 months has matured slowly and is a specialty product.
For selling Shetlands as breeding stock, you are entering a very crowded market, so as an unknown breeder you will not get the best prices for your stock. Better to keep fewer ewes and sell top quality animals as shearlings. That way you can slowly establish yourself as a good breeder.
For worming - for a new breeder, not knowing your land well, you might be best to worm your ewes on delivery, then the lambs either at a couple of months or sooner if they're looking drawn and peaky, or scouring. Our land is remarkably worm free, so we worm at weaning and at point of sale. Other than that, you should start a pattern of sending off FECs (Faecal Egg Count) at regular intervals to monitor your worming needs.