I would like to can many pints of spaghetti sauce, if possible, as store-bought took a nose dive when oil speculation got out of hand around '07-08, and that quality has stayed poor. Supermarket tomatoes, by and large, are also hardly even worth adding to salads, much less trying to make sauce out of. Mountains of local ugly tomatoes are what I want
Make sure to check the jars for nicks, scratches, and other imperfections. These can be bad news for home canning. If any of the jars have these, toss them out.
As for lids, the screw-bands can be used again and again, but the rubber seal parts should really be replaced. I've always thrown them out when I'd open the jar.
One thing I've discovered about canning chili and spaghetti sauce is that during processing, some of the flavor leaks out, so you end up with a slightly bland spaghetti sauce or chili.
There are two options to this:
1. Buy the spaghetti sauce seasoning mix specially made for home canning, which can be costly,
2. Can just the tomato sauce "as-is" (no ingredients added, just tomatoes and salt to taste), then when you're ready to make homemade spaghetti sauce (100 times better than store-bought), just dump a pint or quart or two into the pot, add your spices and other ingredients (if you plan on a chunky sauce with onions, peppers, mushrooms, meat, etc.) and cook.
As for the supermarket tomatoes being sub-par, most varieties found in the supermarket are not of saucing quality. Most tomatoes at the store are meant for slicing or dicing into salads, sammiches, or as a side item. Heirloom varieties are best for saucing. What you want to look for is a lot of "meat" or "flesh" in the inside of the tomato, little to no water, loose skin (easy to peel), and very few to no seeds.
To prevent over-salting or under-salting, and to prevent from it being too "tomato-y" or acidic, do what my mom did: Use a can of supermarket sauce to compare. Once you've got them both matching in taste and everything else, dump the store-bought sauce in with the homemade (cheating, I know, but why let perfectly good sauce go to waste?) and begin canning.