Welcome back!
I vaguely remember you (your name definitely rings a bell).
If you're after the basics, how about you play some recents hacks? The vanilla contest entries of
2014 and
2015 respectively were compiled into collab hacks, and they're great examples not only of what the community is capable of, but also of how sophisticated level design standards have grown. This year's contest is still being compiled into a hack, but the judging's done and you're free to play the entries individually.
Technology-wise, I don't think a lot has changed. (And I guess you don't need to know immediately anyway.) Not sure if you still remember xkas, but it's now been replaced by a more sane and user-friendly assembler called Asar. Similarly, we now have
GPS instead of BTSD for custom blocks, and
AddmusicK for custom music (though as far as I can tell it's not entirely bug-free and the original author's vanished).
Oh, and a lot of cool new additions to Lunar Magic. You'd best check the readme for that.