Visit Hobiecat.com and order a catalogue. It will have diagrams and parts lists for your cat. Hobie will not sell directly to the public, so you must locate a dealer. I've never heard of two side stays per side. I would guess one is a trapeze wire. Trapeze harnesses are listed in the hobie catalogue, but I am sure there are lots of sources for them.
Glad to hear you are going to experience the joys of sailing.