Question: If I'm making Homemade Jams/Preserves, how long will they last?

Answer: 
"Use within a year" is a good guideline. There are exceptions. Lingonberry jam done right is easily good for a couple of years.
There's also freezer jams, which can easily last a few years in a deep-freeze without losing much quality. They're well sealed, so there's little moisture loss / freezer burn, there's little loss of quality aside from the initial freezing, and you don't have to worry about mold or other organism growing in the freezer.