Any Singer attachment should fit any singer machines even older ones. Problem with older one is that the feed dogs may not be drop when doing FMQ. If the feed dogs do not drop then they must be covered with thin plastic/card/paper so they go not move when FMQ.
As to whether generic foot will fit any machine it depends on length of shank. Take your machine to LQS/Sewing shop and have them check different brands. You do not always have to buy from them. Just pick their brains.
I have found that "walking foot" will do straight line stitching but not well and the bobbin thread may not be right tension. For those of you who have not tried/used "walking foot" they make you quilting life so much easier when sewing on quilt sandwiches!