you do NOT
need to have 999,999KW at any one time, you need to SPEND
999,999KW unlocking routes on the "Power Map".
personally i bought the Yoshitmitsu Katana from Meldacio HQ (need Dave Elkton refugee as LEADER), played Roboressurection like the other guide here recommends (fastest hunt with biggest XP/KW payout) until i reached LVL 26-27. then switched to The Injurious Jabberwock until LVL 31 grinding for dragon horns.
up until then i never sold any crafting materials or weapons or anything else, so selling everything except my yoshimitsu and 2x dragon horns i had ALOT of GIL!
the reason you need GIL is because in one of the updates, they added a FISHERMAN in OLD LESTALLUM (after arriving in OL, head to the opposite side and down the stairs on the left and NAVYTH should be to the right.. fishing) 222,000 GIL for 500,000 KW.
after grinding out robo and jabberwock missions to lvl31 i had 7 sigils unlocked and decided to use some KW to clear up the map for schematics and refugees, before i could clear the power map the achievement unlocked. (all before moving to cape caem)
P.S. in case your wondering what the dragon horns are for, they are to make it easy to level up the yoshimitsu katana to Honebami katana LVL 99.
heres how to get the katana (assuming you elected dave elkton)
THEN take the p.ingot and funny bone to dave at the established trading post at Meldacio HQ.
and how to upgrade to honebami
you might also consider only upgrading your weapon when you either have a cid boost to crafting randomly after a mission, or grind out daily missions for elemental stones to purchase a 30% crafting upgrade from lestallum's potion shop behind the steam clean tent. (takes 60 of each crystal to buy the 30% upgrade, you get at least 10 each daily mission) all crafting upgrades are temporary.