Im by no means an expert but have been processing my own deer (usually 2-3 or more) every year for the past 7 years and tinkered with it when I was in HS about 5 or so years before that.
Here's a few things Ive learned as to the quality of your meat.
#1 -- How you harvest the animal. -- Here we have problems with people running them with pickups -- dont do this - its not ethical and the meat will taste like crap when you've ran the animal into the ground, gut shoot it etc.
#2 -- how you field prep the animal -- gut the thing soon after harvest, keep the guts off the meat, dont poke the bladder, be careful about the esophagus leaking gunk on the meat etc. Get it hung and skinned out as quick as you can to get the meat cooled down asap - watch the hairs (others will argue about the skinning but take one that say you skin in 40 degree heat several hours after it has expired -- the meat will still steam -- the hide is nothing more than a bacteria infested blanket - get rid of it.
#3 -- You'll make your life easier processing the meat if you age it. It will make it easier to separate the connective tissue, fat and other crap. What I do is debone or quarter the animal after its hung and cooled and let it sit in a very large cooler (120 qt or larger) for a minimum of a week occasionally draining the water/blood off and adding more ice if neccessary. Make sure the layer of ice on the bottom is plenty thick and then lightly coat it on top. This will help break down the meat, keep it from drying out and help get rid of a lot of blood. I let mine sit for 2 weeks when its colder in the garage. I just call this wet aging.
#3 -- As youve stated, take the time to get rid of the connective tissue, and overall garbage
#4 -- grind away, follow some recipes and have fun
Dont know if I helped much, but Ive made jerky a few times and I am not going to make it anymore. I dont like it very much, and its a complete PAIN in the "bleep" for all the work you have to put in. Everyone will ask for it and its probably something you will have the most time/effort into making. Id only make it if you like eating it.
Snack sticks are easier if you have some good equipment. I make mine in 25 lb batches and have been mixing it with a drill in some sterilized home depot buckets. This year I think Im going to buy a 25lb meat mixer that will attach to my 1hp LEM meat grinder.
The only jerky Ive made has been from ground meat and formed into strips. Ive helped my buddy make muscle jerky and he got it very clean. It will be easier to cut up if you have separated the muscle/roast into its individual muscles
1. How clean does the meat need to be? -- the more time/effort you put into this the better
2. what cuts of venison are best to use? if you're making muscle jerky Id use meat from the rear quarters -- you'd probably need to pull out the muscles you want to use before taking it to the butcher
3. Can/should the trimmings be saved and used in sausage? Im not sure what you mean by trimmings, but Id save any "good meat" and throw any "silverskin" fat or connective tissue you trimmed off away
4. once defrosted can the unused/trimmed meat be refrozen? yes, Id just limit the # of times this happens
Another tip -- pork fat/bacon trimmings work best to mix in fat wise. Ive used beef fat but its a "bleep" to get run through the grinder. Beef fat is only good to use when making hamburger. For everything else Id use pork fat.
I probably didnt directly answer any of your questions and provided too much info but hope it helped a little. Heres the place I buy all of my supplies from. They are just down the street from me so I go to their storefront but the majority of their business is E-commerce --- http://www.waltonsinc.com/
They'll sell all of the supplies, mixes, seasonings, casings you would need.