Regarding the Defiant Bridge: As Owen said, the Helm/Ops positions are indeed combined in one console.
That leaves four other stations, two on each side of the bridge. Generally, two of these are tactical - one on each side to provide redundancy (Not that an exploding console actually ever damages the console - just the ensign!). The remaining two are science and engineering.
Now, this is where it gets interesting. Like most things about the defiant, the console positions change nearly every week. Some of them have also been variously used as comm/medical etc...
Generally, the layout is as follows (From the Captains Point of view facing towards the view screen)
Forward - Helm/Ops
Port forward - Engineering
Port aft - Tactical 2
Starboard forward - Tatical 1
Starboard Aft - Science
Behind the cpt is the situation table and/or holographic communicator as well as Mission Ops and Environment
Now, to finally complicate it even more, when they introduced the Sao Paulo another console was added behind the captains chair - Odo was at it during the final battle for Cardassia, and while it's possible its a tactical station its unlikely because of the fact it provides poor LOS to the main viewscreen - something most other stations seem to have (Though I recall the tactical station on the Enteprise refit in the motion picture being similarly obscured).
Does that help?
Later days!
Mark
'Wish I could Help you....Wish I could tell you,
That I am real, I'm not something you invented,
That I'm not everything you want me to be.'
'And I am...Ageless. And I am....Invincible.'