For survivability, specialise your mage into Knight-Enchanter when the time comes. With fade shield, your damage output becomes your defense by being converted to barrier. Took me a little while to get the hand of this, but once I did my inquisitor became completely unstoppable. Barrier almost never goes down so long as you're outputting damage.
The first time I became aware of how imbalanced the knight-enchanter specialisation is was when I stumbled into aggro range of the Exalted Planes dragon. It was one level higher than my party at the time and I was completely unprepared. I decided to just go for it though. Well, my party wiped inside a minute (or so it felt like) with barely a dent in the dragon's health bar. With only my knight-enchanter left standing, though, I soloed the thing slowly and steadily, only needing a single healing potion when I mistimed a fade cloak to bring my barrier back up. I'm only on hard, but still soloing higher level dragons without any preparation is pretty overpowered I guess.
I've now also put fade-touched obsidian in my crafted armour so that it generates guard on hit and fade-touched iron in my staff so that damage (even to my barrier or guard) heals me. Now this is a bit over the top as it pretty much completely mitigates any risk associated with the build. Even if I screw up, I've still got guard behind my barrier and if I screw up again, I can heal from damage to my barrier once it's back up.
The only challenge is keeping my party all standing, especially Dorian. If I was content to just let him drop in difficult fights it would be extremely straightforward, but hey he's a companion so I feel I have to keep him up and well.
With a good complement of fun spells like fade step, fire mine, static cage and immolate as well as the bread-and-butter spirit blade and fade cloak I'm finding the class quite fun to play as well, flitting around the battlefield like a whirlwind of near indestructible mayhem.
Nearly 90 hours in, only a bit of Emprise and then Hissing Wastes to plow through and then I guess I'll need to finish up the main story (which I'm probably highly over-levelled for now, but hey ho...). Still really enjoying it.