Which materia shall I use?

Hello, I am a Lv 50 Blackmage and I am about to gear for the 50s content. I am going to go the long road and make myself some crafted gear because I was still going to level up all the classes to 50 anyway. So my question is: Which Materia shall I attach to the armor? I think about only attaching Int. raising materia, is this correct or is there any offstats that are better than int or does int stop to matter after a certain number is reached?

Also a subquestion: Which armor is better than the best HQ crafted full gemmed armor if anyone knows that. So I know which armor to grind when I am done with the crafting gear.