About the Kenmore you have--why not post an ISO (in search of) in the buy/sell section of this board. Someone may have a copy of the directions and also attachments they would sell you.
I would not buy a new machine till you have tried quilting with your Kenmore. Lots of people on this board end up using their vintage machines as backups cause the new GOOD machines are very pricey to buy...and to fix. Quilt for a while on the Kenmore, the old reliable, and meanwhile, try out a few machines that are in the price range you are thinking of.
I do all my piecing on a 1950's little singer 99 and my 30 year old Kenmore is fine for free motion quilting with a darning foot. I cover the feed dogs with a thin piece of plastic, and away we go. I just did a twin size quilt on it, and it worked great. It is a trusty friend, and I have never had it to a repair shop..just clean and oil it when needed.