I've searched to no prevail.
What does Light Radius do?

What is Offense vs Attack?

Is there a list of all the mods with descriptions?

Light radius reduces your chance of getting ambushed. Not much else. It's probably one of the least valuable stats, but... it's there.

Honestly attack and offense are almost the same except attack is the value typically used when determining damage. Offense converts to attack 2.4:1 or something like that. I can't remember off the top of my head. I guess classic EQ was kind of the same way. It had attack and offense. One difference is that offense can be increased in the course of leveling while attack cannot.

I can't check at the moment, but there might be a list of descriptions on the poorly maintained wiki.

One thing that might add a a challenge would be increasing the odds of getting adds when in combat. Or does this change at higher levels?

This changes based on difficulty. It also increases in dungeons. I might add more situations in quests where you have to fight two or even three mobs in future patches.

i haven't been noticing very many adds in Hell mode.

Is ambush chance zone dependent or is chance to ambush a mob attribute and say orcs ambush more than gnomes?

Do you have plans of adding light radius debuffs that mobs cast/proc on you to increase your chances of being ambushed?

It's entirely zone dependent. Outdoor zones are very light on ambush. Dungeons are tougher. Harder dungeons have higher ambush rates.

I take it back. I'm pretty sure it's zone dependent only.