1. https://www.wow-freakz.com/spells.php?spell=48108&name=pyroblast & http://wowwiki.wikia.com/wiki/Pyroblast
2. When you receive "Pyroblast!" ( instant pyroblast cast ) and then hardcast a normal pyroblast, the normal pyroblast removes the "Pyroblast!" buff, which means you lose out on 1 extra pyroblast.
3. Upon throwing a hardcasted pyroblast whilst having this buff up you should receive the buff (if it is a critical strike) http://wow.gamepedia.com/Hot_Streak as well as keeping the https://www.wow-freakz.com/spells.php?spell=48108&name=pyroblast and not lose out on that extra pyroblast. This is only if your hardcasted pyroblast is a critical strike that you should receive "Heating up" if it does not crit then you should keep the instant pyroblast and not lose it.
4. 26/03/2017
5. Both
6. 4/10 ( PvE purposes only I guess )