1 - You can start by reading the thousands of documentation in this section :
http://maemo.org/development/

2 - The programming language is up to you to choose, could be
python, C/Cpp... etc. If you know nothing of nothing about these
languages, I suggest you to learn the basics first, how they work,
and all, it's not thaaaat easy. ( Might be for somes, not for me at least =)

3 - Learning curve? You mean how long will it take for you to learn?
Only you can know it...

Hope it helps somehow.

Edit .: Forgot!

This section is also pretty nice if you want to start.