Hi Icarus - thanks for the props!
I was one of the first to get Viking Eddie and have tried lots of combos.
The one I like best and recommend is three Purple (Assassin Barrier) and three Green (Ward)
This is more of a damage build than a tank build, but he seems to do fine with it. Those Mystical Talismans you're using will give him some added DEF, but reduce his damage output. I don't use Mystical on characters where damage is a big part of their role - which I would argue it is with Viking. I only use them in support characters like Visions Eddie - where damage is less of a concern and he's there more for support - like removing effects and cleansing.
He's True Damage but also scales nicely with MR, hence the Barrier and Ward recommendations. It DOES make him more vulnerable to physical attacks however - so swapping out a Barrier for a Shield and a Ward for an Overwhelming would give him a little more DEF with only a small drop in his damage output. You could also tank him up a bit by replacing one of the three Purple with a green, though you'd lose the bonus from the three Assassin Talismans.
As always it's a balance between health and damage output. I tend to always lean towards damage output because it's the most fun for me (I've sharded almost every Gunner and Assassin Eddie I have) but look at his role on your team and see what makes the most sense for you.
Good luck and feel free to post any questions!