Both Optix and I were playing this a month or so ago in general chat, it was pretty fun. Only problem is the game is really buggy (to be expected), and we kept losing trucks. I personally will comeback to it once its a bit more stable, or if there's a sudden impulse within the org to play it.
Given the process, you can be accepted while still a member of other organisations, and a Director/Executive will speak with you to work it out and explain whatever is necessary. But it is expected, like Warpten said, that TA is your main organisation, and you are not affiliated with any organisation that has conflicting interests.
As someone currently studying to be a veterinarian, and have been learning about animal welfare this semester, you've made the right decision Tac, and I respect you even more now. Its a shame to see another loyal soul go, but at least they no longer have to suffer. Take your time to grieve, as I hope everyone can understand that you need the break. We'll all be waiting for you to bounce back in high spirits soon enough!
It could be a nice little cosmetic addition to your profile/citizenship that other players could look up on the web, or whatever the equivalent is of the time. You're given a choice to pick from a bunch of planets as your place of birth, maybe the player is told a bit about these planets. Many MMOs have done this in the past, and often associate your decision with the appearance of your character (LotRO being a good example, where Men could choose to be from Bree, Gondor etc. and it affected their skin and hair palette). This is an MMO, player interaction I hope is going to be a big part, and these kinds of these could help to add depth and immersion to each individual. Unless of course you don't care about player interaction. I reckon it shouldn't be about trying to perfectly optimise your character to suit the role you want in the Persistent Universe, instead, just make the character that you can make a lasting impression with. However, I guess not everyone is particularly interested in the roleplay aspect of the game.