The Star Series SU is a lovely machine,
you can purchase a manual from here - well worth spending the dollars to find out how it works, especially the buttonhole which isn't like modern 4 step ones. You may also find that the foot control has a switch to give you slow speed vs normal speed sewing.
If you are in the USA you could also visit www.whitesewingcenter.com
, they have lots of Swiss Elna goodies for sale and are very knowledgable on these machines.
You might also want to track down a newer Swiss made Elna pressure foot holder with the clip on feet, rather than using the full feet with your machine. They are interchangeable. Have you got the black discs to go with your SU too? there is a large range so you can sometimes track down some more to add to your collection.
There is also a newer black pressure foot screw which is a combined thread snip, its a bit bigger in diameter to the black thumb screw on your machine now and you can use it to cut and hold the threads at the end of each seam, very cute.
Always give this machine a good clean and oil before using it, there should be a red dot in the middle of the bobbin holder, oil here regularly and any other points that the manual shows with good quality sewing machine oil, it takes 130/705H standard sewing machine needles, put in a new needle for each project to get great stitching results.
Enjoy your SU!