TheLastOne
Person of impeccable tastes (for destruction)
Discussed here and in the following post. Administered Worlds have to have certain quality-of-life and legal standards - these are required to join the TSAB and falling short of them can lead to sanctions, intervention and eventually dismissal. If there are active wars going on, the TSAB will probably require them to be resolved before the planet can join - but remember that Earth is pretty overpopulated by dimensional standards, and most planets have a far, far lower population due to the increased living space made available by other worlds (also all the apocalypses and gigadeath events in relatively recent dimensional history).
Earth would hopelessly and hilariously fail to qualify on even some of the most basic requirements for TSAB membership - even if you look only at First World countries, most of them have poverty conditions for parts of the population that don't live up to the quality-of-life expectations for an Administered World. The attitude from significant parts of the TSAB would, in fact, stand a decent chance of mirroring the kind of comments made about "African nations with starving children/poverty". Including the part where said comments ignore that a) Africa is not one country, it's a lot of different nations (most of which the person making the comment probably can't name) and b) quite a few of them actually have rising GDPs, steadily improving laws and decent representation in their governments.
In practice, the answers to the first two questions are irrelevant because the third answer is "hell no". Who would go to the trouble of travelling a minimum of 5 light years to the closest star - when you can't go FTL - to find an uninhabitable world that has no common protein bases even if it's in the Goldilocks zone (which it probably isn't) and which needs to be completely terraformed (which nobody in the modern day has the tech to do) before you can live on it in anything other than sealed habitation domes? When, you know, there are hundreds of Type-1b planets that are completely habitable and ripe for the colonising up for grabs within a light-hour.
There's just no point, because travelling dimensionally to other Earths (and the Types 2-4 that have been terraformed to support a human-friendly ecosystem in the distant past) is far more rewarding in every possible way by several orders of magnitude. Any alien polities orbiting other stars have probably done something similar and spread dimensionally on their homeworlds as well, instead of expanding interstellar.
You know, I know you're never going to touch on something like this, but the idea of one of these polities getting hit by a Gamma-ray burst seems like it could be interesting. Only dimensional sea assets would be left, as all life in the polity in all universes would be wiped out at once with no warning. It's a apocalypses that makes the Al Hazard catastrophe seem like nothing. But the people left would be largely the most technical, people who lived in deep dimensional sea station, people on ships, cargo carriers, and so on.
So they have to rebuild from nothing. Like, long run they're more likely to fail then succeed, but long odds have rarely been a barrier to a story.