You can technically infuse up to five types of materia. It's just that two is the ideal to maximize the stats players want most, and three is the more affordable route to decently raise three stats and not have to spend Tier IV materia.

I can't give recommendations on BLM stats. I only know that BLMs have more varied builds than most.
Like determination is always a safe stat, and hence is generally the most expensive since every job can make use of it.
Similarly, crit is popular for being another stat that more directly boosts your damage. Last I recall, about 14-15 points translates to about 1% crit rate.
But BLMs additionally have been able to make use of spell speed and PIE in some builds. Both of them require heavy stacking to see appreciable results. I know the idea behind PIE was to increase your maxMP enough to fit another Fire into a rotation, but that takes a lot of crafted gear and planning.

Regarding the daily quest, there should've been an NPC (Ealdwine?) with a quest right next to Jalzahn in North Shroud. And he directs you to Brangwine for the daily quest in Mor Dhona.