While I'm not a 3DS dev, I've done some game modding and tutorials among other various things.
A) The way I think of it is, you produce something in the hope that it will lead to others producing something. Sometimes it's due to somebody else releasing something, which leads you to into making something yourself. If you enjoy what you're doing, it really shouldn't be about money. Overall, releasing your work for free helps the community to learn and grow.
B) This is true. Devs, modders, and pretty much everyone doing something as a hobby enjoy improving. Learning is a big aspect of it as well. You'll likely learn something new while working on these projects, which helps you to improve.
C) This depends on the dev. Some people love seeing people using and asking about their work. Others start getting annoyed after getting bombarded with the same or stupid questions, which causes them to lose desire to work on their project. Demanding a better product isn't ok. The dev released it for free, and they don't owe anybody anything. Making suggestions is ok though (i.e. "Hurry up and do this!" is not ok; "it would be cool if you added this!" is ok).
