So many questions, so few answers I can give....
1) In theory, yes, Sheridan should be around for the rest of the arc.
2) O'Hare is currently doing network guest-starring roles that will
give him broader appeal (for instance, playing a great bad-guy on a coming
episode of the Cosby Mysteries).
3) Senator Hidoshi is out of office.
4) Background walla is done by the background walla group.
5) You won't see Minbar this season, but you will almost certainly
see it the first part of next season. You will, however, see Centauri
Prime this season.
6) Lots of things will go BOOM soon.
7) The mess hall food is pretty good.
8) The D.Duck poster came from Warners, when we arranged (after much
negotiation) to get the rights to use his character. (This is the first
series, apparently, given the rights to do so.)