I always wanted to weigh everything that came from the garden so I could see how many pounds we grew. The day that we picked 70 cucumbers I decided that it really wasn't worth the time trying to weigh it.
I did make 80 pints of salsa one year - never want to go through that again. That was back when I was chopping everything by hand. Agh. I sat in the middle of the green bean patch and almost cried. I had just picked a 5 gallon bucket full, had more to pick, another bucketful in the house and the neighbors didn't want any more.
I didn't have a seperate freezer, didn't have much free time...and never have had a garden like that again.
Last year I figured this for tomato/spaghetti sauce. We use two quarts per dinner X 52 dinners(once a week)= 104. I ended up with 54 after my tomatoes failed. But we made it until about a month ago. So I kinda figure how much we use of something per week then times it out.
Someone around here said "100 of everything". Which seems like a good goal to me.
My canning usually follows how much of something I have and how bountiful the garden is. A couple years ago I made so much zucchini relish I had it coming out my ears. Never again.
I would make a list of what your going to can and guesstimate how much you will eat. Its a good starting point.