Fog has its own weather effect, there's no real need for an image.. unless you want changing directions or something, because it only seems to scroll left slowly.

Lag = Lack of RAM, I think. Can't do much about that, as I've said before RPG Maker isn't known for its efficiency. Try running it in full screen mode to see what happens. The lag also might simply be caused by too many Parallel Process events in the background, use switches to turn them on/off.

Lighted torches can simply be set up as a charset with 4 frames (left/top/right/down). Unless you're saying you want the actual LIGHTING from the torches, like yellow circles around them or something.. if the lag becomes a problem (and it's not Parallel Process events that's causing it), cut down on the number of torches or turn "off" the pictures that aren't currently on the screen - no need to have torches running 100 steps off screen.