You should find your answer in the DoH sub-forum. I haven't reached the 2.4 crafting myself, but from what I know about it (not 100% sure):
1/ You will need the artisan gear/offhand fully melded to be able to reach the requirement for 4 star crafting
2/ There are cap (as for BiS 2.3 gear too), normally the order you meld them based on the price of those materia (like +Control first since they are damn expensive etc.) You can see the information about gear here: http://ffxiv.ariyala.com/Goldsmith