What I'm wondering is wherther one affects the number of mobs I can have around me. They don't despawn until you hit them so they will have a cumulative effect unless you clear them out.
I don't believe so. I had about 10 or so floating around an area I've been working. Entcount was 42. After I shot them all with arrows, entcount remained the same. You should see our test environment, there is a chunk that's LOADED with fireballs. Excellent target practice.
Resources mostly and laziness. I dont feel like slabbing everything. I ensure the maximum number of spawns by doing 180 block radius.
I thought Aikar said the current spawn radius was 5 chunks. Is there a reason you're going so far out or am I missing something?
I don't think that the mob spawnings are changed, since I was being attacked by two ghasts at the same time in the nether....