I taught myself to tie sausages using a YouTube video
Yep - me too. There seems to be very little you can't learn via YouTube (some that you certainly don't want to!!!). I have taught myself sausage making and tying (there's a few absolutely amazing videos where the butchers hands fly so fast you can only see a blur), new knitting techniques, hand carding, drum carding, making fudge, braiding, removing ticks - all sorts!
I really don't think you need to go on a course for sausage making specifically - perhaps if it were part of a butchery course, or curing and salami making, but it is actually quite straightforward and once you buy your sausage stuffer you will never look back! Good luck!