Hello and we are happy to see another part author 
First of all I like to answer your question for the Part tracker (PT).
Please read the section "Submit New Parts" on the page http://www.ldraw.org/library/tracker/
You need to sign the agreement, that is very important.
For your other questions:
2) yes, that filename would be ok, if not already on the pt or official.
3) If you only changed some colors i would leave the author like it is and add your name in the history line.
4) Currently I do not have looked into this, so can not give an answer.
First of all I like to answer your question for the Part tracker (PT).
Please read the section "Submit New Parts" on the page http://www.ldraw.org/library/tracker/
You need to sign the agreement, that is very important.
For your other questions:
2) yes, that filename would be ok, if not already on the pt or official.
3) If you only changed some colors i would leave the author like it is and add your name in the history line.
4) Currently I do not have looked into this, so can not give an answer.