1). Everyone is a newbie at some point 
. You need to decide what type of plugin you are going to create, i.e. what type of learning activity is it going to be. So my speciality is towards question types. Creating a question type means you can take advantage of existing code for things like marking and starting saving and backing up instance etc. However you might want to look at other plugin types such as the assignment or assignment submission type.
2) Advanced developers generally spend their time developing rather than writing about it so your best source of inspiration is the source code from plugins. Download and read through things that do something like what you are trying to do. You might consider this book
https://leanpub.com/moodle
The author is a very experienced Moodle developer and I have been slowly reading through it for a while and it looks good.
3) I don't quite understand this question. Moodle comes with the source code under the GPL license so you can do just about anything you want with it on your own machines.
4). I am not entirely sure I understood this. If you create something and you think it is good then you are encouraged to submit it to the Moodle plugins database. It will be checked to ensure it doesn't do anything bad such as make a users system insecure and then it will be made available for anyone else to download. The benefit for you is you get to make the world a slightly better place and it might give you some extra influence when applying for a job or writing a resume.
Normally you would test any code extensively on your own installation, in fact you would do the development on an instance of Moodle on your own machine. So I have a Windows Laptop with WAMPP and constantly install and uninstall versions of Moodle and different plugins. (I am not reccomending WAMP by the way, I just happen to use it).
I hope that helps, but I expect I will have raised lots more questions. Tell us more about what you are thinking of creating.
Good luck
