Have u ever went to the fallout wiki, most of your questions are very well answered there
Here have a link:
http://fallout.wikia.com/wiki/Fallout_Wiki
Now if u want to debate those questions:
Does it matter who droped the nukes in 1st place? the world "ended" in 2 hours, when fire is raining from the sky u dont care to think about why and who, just about where to run. But everything points for a chinese attack( even though the megaton bomb is equal the bombs u find in fort constantine, maybe a crashed plaine, miss caulculations who knows...).
The vault experiments were not Big brother, they didnt had cameras watching ppl, and the enclave could care less for the way they were living they just wanted the rusults of the experiments, like the one from vault 106 with the psicothic drugs released in the air system or the Necropolis vault that never closed and flood the vault with radiation creating the ghouls from fallout 1.
About harold if im not wrong in the end of fallout 2, there was something about the tree in his head growing and giving fruits or something like that, long time i played fallout 2( it was my 200th time and i cant remember) :fallout:
the cars that explode and the fat man were not nice in my opinion but i never use the fat man, its not as fun as melt ppl into a pile of goo.
The vault dweller from fallout never abandoned anything he was kicked off, exiled becasue he was a hero. He changed too much in the time he spent in the wastes and the overseer thought that it wouldn't be nice for the vault, like the overseer says in the end: Ppl will make u too many questions... The ppl could think about leaving the vault and [censored] up the experiment( i believe all the overseers knew about the experiments). So the vault dweller left with nothing but his bare hands, i think it was a lot for him to creat a tribal vilage.
This are the answers i can give u, not much because its been a while i dont read about the fallout lore, or play the games and becasue fallout 3 is too addicting
PS: The enclave could care less about supermutants and what happens in the wasteland they just want to exterminate everyone that is not pure as em. ALso they were in the middle of the PAcific in the oil plataform, dont think they would bother to go fight super mutants.
Sorry for my bad english