Melding is a bit tricky since we don't know the next requirements. Right now on my tools I only have CP melded onto each (with the rest blank) because fundamentally I don't need the other melds yet (and often still don't when the next tier comes out). Often times what I recommend to others is you can plan to do "sub-optimal" melds on a few of your other items and then meld that extra bit on your tools.

My overall melding advice to most right now is meld one V materia into each BIS piece, IV into the remaining garenteed slots and then whatever is reasonably priced into the overmelds and you should be fine for four star crafting when released. I'll have to make an optimal melds, and cheep meld recommendations when four star releases!