It's a simple choice:

[Whateverist]

Basically what it means is either you serve yourself, or you serve others and God. By serving others through God, you serve yourself because we are all one. However if you only serve yourself, you can't serve others and God. God wants us to serve others, because in the end we grow ourselves while we grow others towards God.

I do appreciate the simple transparency in your rephrasing of MK's post.  In essence you're saying, serve the good of the whole and you will serve yourself in a fitting measure.  

I've got to say though "serve" is a loaded word.  It implies I am humbling myself to another.  And why should I do this?  The implication in your proposition is that one humbles ones self in order to exalt one's self.  So ultimately the appeal is to self interest even if one would like to call it enlightened self interest.

How am I to serve others?  The usual suggestion is that one ought do unto others as one would have them do unto you.  But can we assume that everyone is wired to want the same sort of  doing-unto?  Some doing-unto can feel oppressive to the one being done unto, to the point of interfering with that ones ability to pursue his own chosen projects.  For some of us, it would be better to say "do not interfere with others in the manner you would like them not to interfere with you".

It is very hard to know what everyone would like done unto them.  Hell, it can even be hard to know what one would like to receive.  In the end, wouldn't it just be simpler if everyone gave others the space to do as they like .. along with the means to the degree that is much needed and to do so would not undermine ones ability to go on pursuing ones own project?

In the end it is the question of how much one ought to share the means they control with others who have less.  If your excess means are limited, then how much and with whom do you share?  And how far down ought one draw down their own means for the benefit of others?  What if the amount of crushing need far exceeds ones ability to contribute?  The OP's simple, general questions and your own rephrasing of them lead to more complicated and specific questions, to which I do not have the answers.  But neither do I accept the authority of any religion or system of beliefs to decide them for me.