Mint on its own, whether fresh or dried, is seriously disappointing. It adds nothing whatsoever to the flavour. If you want a herb sausage, you could use a generous amount of Herbes de Provence and black pepper which go so well with mutton/hogget/lamb.
I have used apricots, minced, with Moroccan spices which were fairly nice, but my favourite is hot chilli. Lakeland also do a good spicy sausage mix which goes very well with sheep meat.
If you are making the sausages yourself, and are trying to work out how much flavouring to use, then imagine how much you want per sausage, and work up from there. As you add the herbs and spices, test fry a spoonful to see if you've got it right.
I don't add fat and as my sheep are primitives which carry very little body fat, the sausages can be a little dry. They benefit from the addition of rusk, or you can make a spelt loaf and use the crumbs from that.