1) All planets look like California (with same gravity, air, food, etc.).
2) Alien species are different from humans in appearance only. Aside from that they live and mix together much more easily than humans from different ethnic groups do in real life.
3) Starships no bigger than a car cross the galaxy (I mean: hundreds of light years of empty void) just as easily as you take your car to go from San Diego to L.A.
1)

Hoth is the same as Tatooine? Coruscant is the same as Dagobah?
2) First of all, your posit about real life is false. The reason these diverse species mix together so well is because if you don't learn to be a little tolerant of a little weirdness, you might get killed--there's lots of weird looking aliens who are really strong--Wookies for example.
Another thing to understand is that the Old Republic lasted for thousands of years [~3000 I think]. Before that, there is several thousands years of history where technology is still well above our current level--before that, history is forgotten.
The bottom line: Alien species have been living together for thousands of years, if not more, and so differences are less meaningful.
As for the aliens being the same "in appearance only"--Star Wars isn't about the
place, it's about
what happens, so naturally illustrating the differences isn't necessary and so it isn't done.
3) First of all, the ships don't travel through the void. They travel through hyperspace.
Second, try going from San Diego to L.A. without leaving your car or opening the windows. Hypothetically possible, but extremely uncomfortable, right?
Thats why you don't usually see snubfighters as intersystem travel--too small, no showers, etc.
As for "hundreds of light years", I don't remember distances ever really being mentioned in anything I've ever read in the Star Wars universe.