#1
I like to use Ernie Ball Hybrid Slinky Bass strings on my bass, but I prefer to use the E string from an Ernie Ball Power Slinky Bass string set (I'm not really sure why, I just prefer it), does this matter?

Ibanez K5
Warwick Rockbass Vampyre 4

Line 6 Bass Pod XT Live
Epiphone Les Paul Custom
#2
It won't really matter as long as the set of gauges isn't too far off. The only thing that matters is the potential cost of having to buy 2 sets of strings every time you restring and using only one string from one of the sets. It won't matter to the bass at all though.