I bought a Meyer lemon plant last year, and don't see any future in actually getting any fruit from it (even thought it came with one, attached). At least not anytime soon.

Vodka has a taste of its own, so I wouldn't use that for limoncello - but as you said, if that's all you can find, then that's gotta do. At least use 100 proof vodka, and I'd let it steep longer than 40 days probably. Unless you just want to flavor the vodka (as opposed to making limoncello)....