I have not done any major restore at all but in my opinion pretty much everything you need by way of knowledge is online and in forums these days. For major restorations what you probably need is an electrician license if you are intent on doing everything yourself. the rest comes from research and interest on your part. There probably are courses on basic understanding of what an espresso machine entails and the major differences between categories as well as maintenance. I am sure the Site Sponsors can help on such courses.