How can I get holes in curved surface in a way that keeps the surface smooth and has a hard edge at the hole.
There are quite a few threads in this forum dealing with this. The one that immediately comes to mind is Jay's spitfire WIP. Around page 7 we kind of hijacked his WIP thread to discuss how to get holes in curved surfaces.
I'm not in the industry so I never went on any official training courses. Most of what I learned over the years is actually from this site. There are a good number of very good tutorials here. The instructors are good and do give a lot of tips and tricks on how to do things. I also found that having a look at other peoples' WIPs gives one lots of hints on how to do things. A person might have a problem with some topology and I've found that there are always people here to help out with advice.
So whenever you get stuck with something, post a note here and the guys and gals here will gladly help out.
Earth: The crazy asylum of the universe.