#1
Hey, I'm new here so sorry if I looked over some blatently obvious answer to my question...

When tuning a step down on a 5 string bass, what are some possible tuning combinations for the 4th and 5th strings?
#2
I'm not sure what you're actually asking. If you're tuning a step down, then you should tune all of the strings a step down. There isn't really any special way that you can tune those strings, other than a step down (if thats the tuning you want).
#3
You can tune to any notes you want to, really.

On a 5-string, cats sometimes downtune the B to an A
AEADG
or tune the E to a D
BDADG
or even both
ADADG

You just have to get used to where the notes are when your playing in those tunings.