I wrote this up in another post in december - gonna copy paste. I hope it clears up some stuff about the (5) reactor. Will try to get around your other questions as soon as I can:)
This is gonna be a long explanation ichiban but let me give it a go.
SOME items are born with specifix SET affixes - like this one:
If you want a specific set item for your gear - you can farm for those specific legend items - OR you can put a set item affix on your gear, by applying a CRYSTAL:
How to apply crystal you might ask?
There can only be a TOTAL of 6 affixes on your gear - empty socketable = an affix. Also, there can ONLY be ONE set affix on your gear.
SO - if you wanna add a specific SET affix to your gear using a ruby - first of all make sure there is no other set affix(green) on the item and make sure that there is only 5 other affixes on the item.
IF you wanna remove a set affix from an item - use a KYANITE. Kyanite can also remove other affixes - except the blue ones:
IF you have 5 affixes - and no other set(green) affix on the item - you can use a ruby on the item. The ruby will NOT ALWAYS give you the exact set affix that you want, but it will give you some different choices from all of the set-affix options there is. So IF you are lucky, then ruby will make it possible for you to apply the set affix you want - but its about luck:)
So you might end up farming a lot trying to reach your goal, and sometimes its easier to farm for a specific LEGEND(red) item that is born with the affix you want, instead of trying to get it with a ruby,
In general about set affixes - the bonus they give becomes better, the more of a specific set you have equipped.
So ONE piece of 'FAUN'S GIFTS' will be displayed like this on your item:
(1) FAUN'S GIFTS
TWO pieces with a (2), etc. Every added piece will give you more of the bonus that the set piece gives - for FAUN'S GIFTS its this (blue box the bonus) (red box - the number increasing if the (X) number is raised):
You dont HAVE to equip 6 pieces of FAUN'S GIFTS to reach (6), as there are legend affixes and mythstones that gives you up to +4:
That said - you can ONLY have a total addition of +4 from bonuses like the two I just described. Some ETERNAL(green items) can give you +4 also - but no matter what - you can NOT get above +4 set bonus.
So - if you wanted to reach (6) FAUN'S GIFTS you would need 2 piedes of gear with the set affix 'FAUN'S GIFTS' = 2
and combined +4 set numbers, as examplified above = 4
all in all =(6)
You can of course have 4 set pieces and +2 set numbers also if you prefer that option.
Sry bout the wall of text - but I hope it can help explain. If you want me to clarify something - let me know. And I might have gotten some of it wrong - but thats about it to my knowledge:)