1. About yellow hit cap
A lot of people on Nostalrius told me that the yellow hit cap is 14%. Any idea why so many people say that, as it seems clear after having read all of this that it's 8 or 9% ?
8% for melee yellow attacks. 14% is spell hit cap
Second point : in the end, is the following statement true or false : "There is always a 1% chance to miss and a 1% chance for spells to resist in vanilla." ?
1% chance to miss against NPCs, yes. This only applies to spells
Third point, some people told me that this cap depends on the boss we are fighting. Is it true or are all the raid bosses level 63 with 315 skill ?
All bosses are lvl 63 / 315 defense
2. About stats
A lot of people told me : "in sword spec you must favor AP, but in dagger spec must favor crit". It seems like no one mentionned that here. Is it true ? And if yes, what are the reasons, exactly ?
Not really true. Plug your weapons and armor into Soyeon's spreadsheet to see what is an upgrade for your DPS.
3. About OH weapon speed
I read that instant poison is implemented with a PPM, which means that a fast weapon won't proc more often. I was then wondering : what would be the purpose of having a fast OH weapon ?
Crippling poison is a %chance to apply, so a fast OH is very nice for PvP. Instant poison is not affected. Sword rogues will want a fast OH, since Sword Specialization procs on a %chance and swings with your MH, even if it procs off an OH swing. Dagger rogues do not care about OH speed in PvE.
Normalization only applies to instant attacks ie SS, which are main hand swings. You still want a slow MH. It still does more damage after Normalization, but doesn't double-dip from AP scaling