As I recall, the Janome 1600P needs to have a cover for the feed dogs when FMQ since they don’t lower on that machine. You can get A new Brother PQ1500s (basically the same machine) for about that price and it has the ability to lower the feed dogs. For just a little more, you can get a new Juki 2000qi or a New Juki2010q. Both are also pretty much the same as the Janome but they can also Lowe the feed dogs.
the going rate for a used PQ1500s is about $350. If the Janome 1600p looks a little rough I would not pay anywhere near$600 for it. If you do decide to go for it make sure it includes the cover for the feed dogs— you will need that for frame quilting.
Rob