Time spent until some milestone is highly dependent on the person.
For opposite cross, solve always with the new colour until you're comfortable with it. Then flip a coin to choose which cross till you can switch between colours comfortably. Then pick the best cross.
nope! that's impossible.
if you need such an algorithm, i think you haven't solved the other centers correctly. re check them.
I have experienced the same thing and asked this same question in this thread before.
well... actually you can rotate it 90 degrees, by doing (U-perm)3 but that way except that center, the F center also rotates 90 degrees but you can't see it because it doesn't have a logo on it!
I'm experimenting with that right now actually. Trying to see if it's ever necessary to rotate it only 90 degrees. If not then that makes things a lot simpler. I'm going to keep solving my Axis cube and see if it ever comes up. If not then i'm set.
Update: Looking at the textures on my mirror blocks there are 4 pieces that need to be rotated in 90 degrees, so an algorithm that does that really is necessary. I'm looking over that page right now. Thanks guys.