Magic mastery is +10 MP each rank till rank 9, then it adds +1 int as well.
I would reccommend getting at least a few ranks in it, especially if you get advanced magic.
I have rank A so I can cast all 5 MP-consuming thunder charges without using an MP pot (110mp total)
Get at least rank 2, preferably rank 1 spirit of order before advancing any other pally skills
Passive defense skills really don't make much of a difference - 10/15/15% reduction at rank F for HS/NS/MR, 20/30/30% at rank 1, while Spirit of Order jumps from 220/105/520 HP/MP/SP to 650/300/1200
Baol infiltration tomorrow. Hopefully I can do it so I can get rid of the ugly anti-fomor robe.