It'll likely last longer than you will let it. The longest Ive had mine in is a year. Ate up the last of the previous year before I put the fresh batch in.
And...yes you can do it from the freezer just fine. I usually chill mine in the freezer for a while since it makes it so you can just pick up the butter and slice the goo off the bottom. Less mess and fussing. Just dont let the water freeze completely solid.