I'm thinking of creating a half-elven mindblade who will heavily focus on Int over any physical stats, making use of elven battle style to maintain damage potential despite a mediocre strength stat.
I'm not sure what psychic spells to pick up, and can't decide if I want to spend the feats to get heavy armour or a two level dip into student of war to replace my dex mod with my int mod for my AC.
I'm also not sure if I should even bother trying to two weapon fight with longswords or rapiers, or just switch between a single longsword and an elven curve blade (or branched spear) depending on if I need to use spell combat in a given round while waiting for level 13. Is there anything more reliable than spamming blade tutor's spirit to make dual-wielding longswords remotely viable?
Possessed hand + hand's autonomy, and/or using effortless lace (assuming non-PFS since you mention level 13) can cut down the penalties for using a couple of longswords. One mind blade and one normal would allow use of the lace.
I definitely wouldn't choose to drop two magus levels for int to AC. That's nearly a spell level lost besides the delay in other class features. Weapon finesse and a decent dex will be easier than using heavy armour IMO since you'll need at least some dex just to get the TWF feats.
On psychic spells, burst of adrenaline (1), false life (2), strangling hair or greater stunning barrier (3) and calcific touch (4) all look good for a magus. Placebo effect will let you cast when shaken or similar and you might fill out the rest with utility spells.
Don't have much need for Dex; Artful Dodge would let me into the TWF chain based on Int.
Having built both ways, I'm really liking the defensiveness of the Student of War. Given how easily my current character is getting smacked around in Giantslayer (despite having been built prioritizing defense over offense), having a character who starts at 30 AC without any particular effort is very appealing. Artful Dodge, Ironskin, Shield, and Blade Tutor's Spirit + Combat Expertise mean that I could get that up to 42 fairly quickly if I needed to. Throw Mirror Image and Haste on top and I think I might have something that could actually stand up to the ridiculous enemies in that AP.
Burst of Adrenaline might be good, except that my physical stats won't matter all that much anyhow. False Life is good, I've currently got Silence and Ironskin as my two second level spells. Not sure if I want to replace one of them. Calcific Touch will certainly be one of the spells chosen for fourth level.