Normally shoulder is used for sausages, if you're doing it with a Kenwood have the cubed meat almost frozen before you start (it'll mince easier and the texture will be better)
You want 80% meat to 20% fat roughly (might need to add some belly pork if you're short) and approximately 10% of the weight in rusk and the same (approx) ice cold water.
Mince your meat and fat into a bowl sitting on ice, mix the rusk, flavourings and the ice water to bind it all (you might not need it all) and chill again - don't let it get warm or the texture will be peculiar
For flavourings, the choice is yours! I use about 10g of salt and 5g of pepper for each kilo of meat then add whatever you want - minced onion, sage, apple......it's an endless list
HTH
Karen