Welcome to TOG first of all!
Hope you're settling in slowly... bit daunting at first!
To answer your main question, once you're a TOG member (which you are!) you're allowed to wear your TOG tags with pride. Generally speaking, the "correct" way of hanging them is with the "pipe" symbol. For example you'd see me as TOG|Spectre8 in-game. However, some games don't let you use the pipe symbol, and others it creates conflicts... While you'll never be wrong wearing them that way, it's always handy to check in the specific Division.
You seem to have very similar tastes in gaming to me, but I've never sampled Tabula Rasa, it'll be interesting to see how it all goes!
As for "signing-up" with the various Divisions, there's no need to do so until you are ready. Feel free to jump into any Division, post up saying g'day, and the Division Captain will no doubt take it from there.
Hope that answers your questions
Best of luck, and welcome again to TOG!