Q: When you have an occasional note below E and don't have time to open the E latch and close it where ever, can you open the E and finger the note without the other latches getting in the way? Can it be used either way? Closed or open like a single latch?
A: If I have a passage coming up with, say, a D, I open the system to the D before the passage starts. The key is always preparation for the upcoming passage, which is really pretty easy. And yes, the four (or five) chromatic latches all work the same as a single latch on a (totally) fingered extension.
Q: Do the other latches make any noise regardless of what position they are in?
A: Not on my chromatic extension. I can't speak for others. It's probably obvious, but you shouldn't bother getting any extension unless it's being done by someone who knows what s/he's doing. Mike Shank made mine, and I'm going to have him put one on the Pfret too, after this latest experience. I know other luthiers also do good versions, all of which vary somewhat.
Q: If I am getting a 5-string down the road anyway, would the 5er be better for moving passages and use the single latch Extension when it would be usable or do you still think chromatic is the only way to go?
A: Good question. If I were sure I were getting a 5-string in the foreseeable future, I might try to tough it out with the fingered extension. I suspect that a good 5 in the hands of someone who knew how to play one would always be better for moving passages than any other option (except maybe a 4 tuned in fifths). But there's a big difference between a five and any four. Some people never get used to the five-string setup, and others thrive on it. I haven't given a five a serious look yet, but someday I will.
I will say, though, that in my opinion a chromatic extension is a far better option than a fingered extension as one's ONLY access to the low C, unless you're very good and willing to put in a lot of time practicing sub-E fingering (as some do).
Good luck.