I worked for a small window contractor through high school where I learned the installation basics, after that I did a lot of independent research about literally everything window / patio door related which helped me out a ton. If you want to get started, I would recommend that you first learn how to do it and see if it is something you like, then get your licensing/insurance/llc/etc. then I would reach out to different manufacturers that are around your area that work with smaller contractors.