Hebs are not worth sending to slaughter before 16 months. They don't put on any condition over the winter and need grass into the summer to reach a good weight. We have tried slaughtering at various ages and have found that the best carcase is at 16 months, ie early to mid Aug of the following year from an April lambing. Slaughtering them at weaning wouldn't give you more than a rabbit on a stick

I have never sold Hebs as stores and am not sure what the market would be. It might be best to find a buyer privately, perhaps through the Hebridean Sheep Society. The Nature reserves are often looking for wethers (have to be from registered stock) to Conservation Graze their reserves, so you could perhaps approach some of them if you don't want to raise them for meat yourself - which would be a loss as they are very very tasty
As we breed breeding stock, we don't castrate our males, except a few with an obvious fault at birth, so we take them off the mothers by the end of August to avoid the chance of unwanted matings. We put them in with the stock tups across the road and there isn't much upset at all - they are so busy avoiding being 'checked out' by the big boys that they forget all about their dams
The ewe lambs we tend to leave with their dams for a couple of weeks more. In theory this could increase the chance of mastitis but

we have never had that problem. We then put the ewe lambs into an adjoining field, so they can see their mothers, and graze and lie next to them, but they can't feed, so absolutely no stress. That gives the ewes a couple of months to get back into breeding condition before the tup goes in in Nov. We find that we don't need to dry the ewes off as they have just about done it themselves by the time their lambs are 5 months, although of course we do keep an eye on them.
After tupping, we run all the females together again, and all the males in a separate group across the road. After the first season when the tup is on his own, there will always be enough males waiting to see if they are good enough for breeding stock, or to go to slaughter, that the breeding boys always have company. The ones for slaughter go in early Aug, the grass has a couple of weeks to recover and then the male lambs, now hoggs, arrive in that field.