LOL! Good call, Gidde. Yes, Hardness is the first thing to look at. As you can see from my list above, I tend to go for the harder end, so I might not be so much help after all, but just a few pointers to get you figuring where you want to go:

If you're going for the softer sci-fi, technology can be almost anything you want - and if you're going for an intergalactic campaign it'll be well off my scale. Galaxies are several million light years apart (compared with several light years for interstellar distances) so if you want to get there in less than a year, you have to be travelling at several million times light speed. What tech would accomplish that is anyone's guess - and by the time humans have achived that level, they might not even be recognisably human... But I'm talking hard sci and logic again.

Human governments run the gamut from a single ruler to a council and from participative democracy to totalitarian regimes - pretty much anything goes there.

Aliens will all have the same ecological problems that we're familiar with - the need to respire, to feed, to procreate and to manipulate their environment. You can go for 'rubber suit' aliens or more exotic types, but the less human they are, the more difficult it becomes to explain their motives - even the motive for conflict. The thing that really makes aliens alien is the way they think.

A human invasion of another galaxy (or even a starsystem) would be a huge undertaking that would require huge resources and a very long period of time. It would have the same difficulties, risks and consequences as any other all-out war - both sides risk genocide and extinction.

Hope that helps.