I'm tempted to open a game (likely Psi World) but looking through the systems and such it's actually a rather daunting prospect.  Is there anything like a "New GM Mentoring Service" where someone new to setting up a game can bring in an experienced hand as a consultant who can advise and help with the systems, the administration, etc. until the newbie gets their wings spread far enough to fly on their own?

You can set up your game, then use the Wanted - GMs forum to advertise for a co-GM to help you.

Depending on the system, you'll either get a lot of help offers or none.  For an epically old game like Psi World... man... you'll either get an old grognard who loves it, or you'll get tumbleweeds.  But don't expect a glut of volunteers.

In your thread title definitely put in "Co-GM Wanted" or something, so people don't skip by thinking you want a full on GM.

Well, I'm not actually looking for a co-GM or the like.  I'm looking for an experienced maker of games here who can guide me through the processes of setting one up.  I'd be running the game, creating content, writing rules summaries, etc. all myself.  But it's sort of a case of me not knowing where to begin, even.

I thought someone set up a game forum on this once...don't know if it got anywhere but maybe worth doing a site search for?

If you need click-by-click instructions for the site, try the RPoL Help link top right. If you need specific advice, search or ask in Game Proposals and Advice. If you need free general tips from experienced GMs, YouTube can probably teach you more than a single random from here, who might not be running the same thing in the same kind of style.

Setup is always a bit daunting, but generally once you're past that it's fine. Draw from your experiences as a player as to what you want a game to be, and let your players know you're new to a system and things should get easier as you go.

In reply to Z.Dianli (msg # 4):

You can explain that in the ad.  Most of the games I've been in which had a co-GM didn't use the 2nd GM as extensively as the primary GM...the co-GM was there to handle or advise on certain aspects of the game, and deferred to the primary GM on everything else (except for the game where the primary GM was expecting to be absent for health reasons and added a co-GM to keep the game running in his absence, but that one is an outlier).

It would be perfectly normal to post in the Wanted: GM forum with an ad stating that you're looking to run a game, but you want someone familiar with the process (and/or the system) to walk you through it and advise a bit on adapting to the play-by-post format.  Might even be more likely to get responses to that, as a lot of good GMs will gladly share advice but don't have the time to shoulder yet another game...being involved in a game which they aren't responsible for could be a nice change of pace.

In reply to Z.Dianli (msg # 4):

The Help (link at top right of the screen) explains how to set up a game on RPoL.  It's context sensitive, so whichever screen you are on, clicking on the link will explain how to use that page.

Have you tried the Beginners forum?

I've looked at the Help screens, yes.  Unfortunately, while the information is all there, likely, it suffers from the same problem that most documentation for computer stuff suffers from: it's written by an expert who can't see with the newcomer's eyes.

If I have a specific question about a specific step in the process, the help link is good.  If I don't even know what question I'm supposed to be asking…

This is why I was asking about a mentorship.  Books contain all the knowledge we can get in school, yet we still have teachers, after all.