Hello hello, and welcome back! I remember Valor Eternal by name from bygone days, but I can’t say I’ve seen any of them running around RK5 lately.
These are all understandable questions, and I’ll start by way of sharing a few links to some guides. You’re right: the old guides are a little out of date (NB, the old forums’ profession academies are here), but there are some aspiring tutors out there. 
The indomitable Caloss2 has a wealth of AO tips not limited to the new starter area quests, where things are and how to run AO properly:
Higain’s fr00b engineer guide contains information that can be applied to other professions as well:
And then, of course, if you remember the IP system but need a reminder, here’s a gaggle of people discussing their tastes in IP spending:
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To answer you more directly, MA is as simple and cheap as it gets as a starting profession, and enforcers aren’t too bad either. The good thing about the Subway these days (you will find it in ICC, not in sided cities) is that there are good weapon drops in there, so you might as well pick whatever non-nano profession you like the best and go on a rampage for a while to get your bearings in there. You’ll be looking for “Illegally Modified Ofab …” weapons.
The population on RK5 (a merge of all RK1 and RK2; Die Neue Welt was taken out earlier) depends a lot on what time you’re playing at. A couple of hours ago, I’ve been told, is prime playing time: that said, to a clanner Old Athen rarely seems to sleep, and the same is kind of true about ICC and Borealis. Teaming generally happens either on on LFT (Shift + F opens the LFT window: that must be new to you too) or the old-fashioned way of asking around.
As for orgs, if you’re clanside, Topics tagged recruitment has some obvious examples. On the Omni side, I know about only one org constantly recruiting (they have a recruiting bot set up in OT OOC – can’t miss it); I think the First or Last Element on the neutral side (also have a recruiting bot).
(If you’re a fr00b, give @WAusJackBauer a nudge. He revels in fr00bdom.)
That all said, thanks for reminding me of how it was to hang out in Reets. 
I’m well and truly familiar with how you feel about other MMOs with their one-track mind professions…
And lest I forget, the Semi-Official Anarchy Online Discord server is where you can find some AFKers to ask for buffs and food advice…