• As others have said, the weapon is a secondary thing. If they ask for a gunrun with manpads in the area, you're probably going home in a truck, not your airplane. It is always at the discretion of the pilot what ordnance he releases for a given attack.
• This depends on the mission. On some missions, stingy ordnance management is key, on others, having each plane get rid of it all and RTB for more is the better option. Delivering ordnance on targets is always better than flying back to base with it though. That said, I never jettison ordnance except in emergency situations.
• What you're talking about here is really a strike or interdiction type mission. In those cases, it's really about getting to the destination, finding your targets, eliminating them, and RTB. Often, the allocation of ordnance to tailpipes will be IN the mission briefing, esp. in the case of special ordnance like heavy AGMs (G/K) or 2000 pounders. Otherwise, if there's a JTAC in the area, he's most useful for finding targets that you can't.
• As others have said, CAP/SEAD flights generally won't be operating in the FAC(A) role. SEAD is generally a specific strike mission, CAP is too busy looking for air contacts to worry about what's going on with the ground pounders. The F10 menu is generally just an options menu for mission designers to give various options to pilots. It can also be used for interaction for AI, but even FAC(A)s will show up in the JTAC menu and in terms of the game, will behave exactly the same way as any other JTAC.

I'll think of some more helpful stuff a bit later I hope.