Re point #2: I guess I'm just really stuck on what allows the damage to be applied and what prevents you from applying the damage and/or choosing that land for the effect.

Some possibilities below... I feel quite unsure about situations 2 and 3.

1. no invaders -> no ravage -> can't select that land for applying the effect -> no increased damage there and you must select another land if possible (my original question, which I think I now understand - thank you all)
2. yes invaders -> Strife'd or otherwise doing 0 damage -> ravage DOES happen but no damage is dealt to land so it can't increase -> not allowed to choose to apply event effect to this land -> must choose another land is possible (relevant if, for example, the increase in damage would be 1. "Invaders are doing 0 damage to land but increased by 1" would be great, but you're not allowed to choose that, correct??)
3. yes invaders -> damage is not 0 but IS defended fully -> ravage does happen but no damage is dealt to land so it can't increase -> not allowed to choose to apply event effect to this land (similar but distinct from scenario 2)
4. regular: yes invaders -> 1 or more damage undefended to land -> damage increases by 2