It has taken me years and years, and hundreds of attempts, to get my four variety of sausages exactly the way I want them, both for flavour and texture. We use a heavy duty mincer and mince very coarsely just once, the way we like it. This goes straight in the fridge for cooling while all the ingredients are prepared, onions, apples, herbs, spices, whatever - all of it fresh. It is useful to have a precise set of measurements/weights which you record meticulously each time so that you can duplicate it, or alter it a bit, the next time around. I have found all the pre-mixes very disappointing and tasteless. The only artificial additives are 2 products from Weschenfelders, one their yeastless rusk, and the other a salt and pepper replacement called Gold Pork Seasoning which is absolutely delicious, but must be used in far tinier quantities than they recommend. I use a max. of 8% rusk, very often none at all, all home made bread crumbs have been hopeless, and for very dry ingredient mixes, add a few spoons of iced water just to get the consistency better for stuffing (this is something you just learn over time). In the evening I mix the non-pork ingredients with the mince, then re-chill this overnight before doing my final taste tests in the morning, with little patties of the mix fried up, before starting stuffing. If anything needs a last minute adddition and re-mix - straight back into the fridge for at least an hour before starting to stuff. In other words, keep re-cooling, over and over again, whenever you can.
We have one of those large plastic stuffers which attach to the work surface and the mix gets pushed in with a big manual handle - takes about 3 kg of mix, and far more efficient than the combined mincers/stuffers. In the early days I use to prick the sausages whenever there were air bubbles, but this resulted in them all exploding and falling to pieces when they got cooked. I now just leave any air bubbles and eventually they disappear. I also find it really helpful to hang them up in open, cold, moving air for a few hours (a fan if necessary) to help dry them out before packaging. Makes a huge difference to the final taste and appearance in their packs. We freeze them within 48 hours, and they are absolutely delicious even months and months later.
It is definitely an art worth perfecting - the results are sublime, and exquisitely delicious. Good luck!