All the pieces must be the same rarity.in order to get a set bonus.
So must all be either common/rare/or epic to get the bonuses.
there are only really two bonuses that are even semi worthwhile to use.
TG and SE.
and their are some negatives to both.
Very few Bellagio players play with any kind of set bonus in play.
Also all pieces must be at least level 4.
Hit the circled i where it says set bonus pn any one piece to see the details.
as to how long it takes. at the most a week to get all common pieces in a group to level 4.
Also apparel packs are totally random. You can't choose what sponsor the points go into.