OK, BSG explained:
1.) The nuke blast on Caprica was far enough away that only the shock wave itself actually hit Baltar's home. Its kinda like yer house being hit by a tornado, its gonna mess things up, and you may end up dead or badly injured but it IS possible to survive.
2.) Ron Moore gave an interview just before the finale aired, stating how he had wished that he would have more time/money for the finale to concretely show that the Cylon colony was being sucked toward the Singularity. He said that they had no chance of survival. This can be deduced even from the episode as is, as they talk about how the Colony is the precise, but precarious, position of orbiting the black hole. The nukes from Crashdown (btw LOVED how Crashdown 'saves' the day) send it spiraling (which you do see).
3.) While not each world is explicitly discussed, the general consensus is that the Colonial worlds are not really that lush or temperate. Caprica, and I believe Arelon, were fairly fertile, but overall the Colonies were fairly "barren". This is also noted in Adama's (Roslin?) statement that the continent of Africa alone had more wildlife than the 12 colonies combined.
4.) Adama's statement "1 million LYs" is hyperbole. Also, for those that say, "only one jump from the Colony?"
The actual distance a Jump can cover is not the issue. The problem was the calculations to not a) end up in the middle of the Void and b.) not end up in the middle of an interstellar object. Thus they could only reasonably jump to the edge of their sensors/calculations. For example, if we had Jump technology we could relatively safely Jump anywhere within 20LYs because we have a decent amount of telemetry gathered from observation. But on the far side of the galaxy, its more guess work than actual knowledge. Its the same for the Colonials. Its not that they "couldn't", its out of concern for safety.
5.) God/Gods/etc is, as called by Baltar, a Force of Nature, neither good nor evil. That is, its 'Plan' is to see Creation and the continuation of Creation. The Cycle was one of Creation, but it always ended in Destruction. That is what the Higher Power was working against.