Our family likes about 20% fat content in venison sausage and burger so before deer season I buy pork and beef fat from a local processor. We cut it in grinder size cubes and freeze them on sheet pans after which it gets vacuum bagged in 3# bags. We normally make 15 pounds batches of sausage so the three pound bag of whichever type of fat is appropriate to the recipe is added to 12 # of venison and away we go. As the fat cubes were frozen when bagged it's easy to take out what we need for smaller batches and reseal the bag.
When we use high temp cheese (mostly for regular and venison brats) we use about 5-6% cheese by weight at the very end of mixing to keep it from breaking up.
We generally use standard recipes for venison sausage and haven't seen and issues compared to pork or beef based sausage except that the venison will hold more water than pork or beef (except maybe pasture raised beef) due to the higher myoglobin content of the venison. Generally, the darker the meat, the higher the myoglobin content and the more water it can bind.
I suspect you'll do well to split your next batch and use NFDM in one part and not in the other so you have a better basis for comparison. The process of mixing the sausage releases more proteins so a longer mixing time can help with juiciness and mouth feel. For most sausage I add the ground fat late in the mixing process to reduce the chances of it getting smeared during mixing.
Good luck and let us know when you've got something on the meat pole!