Things I know so far:
-You can get Bahamut and Ultima Weapon from the Deep Sea Reasarch Facility(or something like that) somewhere near Centra I think. These two are GFs.
-Since you have Diablos use his Encounter None ability and start searchinh The Island closest to Hell for invisible draw points( only good magic like ultima, meltdown and so on)
-Death I think you can refine it from curse spikes
-I say that Meteor, Ultima, Triple and Quake(the earthquake spell) are better than death when junctioned on Strenght.

Things I actually did:
- Find Cactuar...there is a small island somwhere in the south....it's really small and it is full of desert....you can see cactuar appearing there from the sand.....be ware....hard battle
- Odin is llocated on Centra....there is a thing...I dunno how to call it....but you can't miss it.....it's like a skycraper in the middle of the desert.
- Tonberry in the same place as Odin. But you have to fight like 18-20 tonnberrys then defeat Tonberry King.
- To get lionheart you need pulse ammo. It can be refined from Energy cristals. Those are very rare. But there is a place in Eshtar....there is a eshter soldier who'se colour is a bit darker than normal...talk to him and he'll say like: Muhhauhwawawhha(or something like that. Then a battle will appear and if you win you'll get like two energy cristals.....repeat the process and you'll have shitloads of pulse ammo.

And I'll think of some more later. Hope it helps.