Not sure I can answer all those questions now, since it will take a while to make a list like that.
But as a start, a DII big man needs have at least 60 ath, and that's a guy who has other skills. A guy with 60 ath but no lp or reb isnt gonna be effective. But once you find a big that's getting into the 70's and up in ath you can sacrifice more on the other ratings but not too much. Speed for big men varies based on the player and type of defense. I only play press on my teams, and I shoot for 30 speed from my bigs, but I'm flexible.
In terms of gaurds, I would let the ath on my gaurds go down to like 50, but you can't play a guard at DII without at least a 70 speed, and that's the absolute minimum.
You definitely need to get all you averages up on that team. Your average ratings need to be high 50's and above in ath/def at least to compete in DII.
If you have more specific questions I can try to answer them later. If you want to look at DII players that I like, look at my CSU Bakersfield team in Allen. I really like that team.
I'm also curious to see what other people look for in their base ratings. Because every time I've seen one of these threads in the forums trentonjoe always comes on and says his base rating are about 10 points higher that what I'm looking for, and I'm always impressed that he can find those players consistently.