Basically with the materia system.

Gear has hidden stat caps, that after you hit that number you can't add anymore to it. Also when melding without a slot the chance of a successful meld changes depending on how many previous un-slotted melds along with the grade of the materia your melding to it(the lower grade the higher the chance). So basically you want to look up the caps and plan out the entire meld before you meld at all, for the least materia lost, do to un-slotted melds along with not wasting higher grade materia.

Also to craft the new 3 star gear. not counting FC or Food Buffs. you need the new main hand tool and head piece and the best of all other gear stat capped, except the off hand tool which just needs a Control III.

There really is no choice anymore expect for off hand tool. with whats needed. So just follow ClaraLux's link and stat cap on full set, then you can skip the head piece for others since the new head piece is universal.