I've been working towards this build for the past three weeks and have now run it around in Orr and some dungeons long enough now to give it a solid thumbs up for the "best feeling" guardian build I've tried yet. When first leveling up my guardian, I _hated_ Greatsword and Staff, lol. Now I love them. So far, the only thing I occasionally swap to is Sceptre/Focus when I need a 1200 range kiting option for those bosses that are too brutal to melee tactics. Otherwise it's 95% greatsword with some rollouts to staff when needed to heal myself and/or teammates that need a little 1400-point boost to help them along until their own healing recharges. I can see the usefulness of a shield in some rare cases too so probably will work on an exo shield/sword combo next.
But ya, I can run around farming in Orr with yellow armor and full Pirate/Traveller runes and do just fine, swapping to exotic Power/Vit/Toughness armor with Soldier Runes for dungeons.
Here's a tip maybe worth adding to your OP for other people? Power/Vit/Toughness armor isn't found on the AH, as you noted in your OP. It can be purchased from two dungeon vendors: AC and SE. At first I thought I was going to have to grind a large number of AC paths to build up the exo armor for this build, but it turns out that the three Karma vendors at the "Cathedral" bases in Straits, Malchor's, and Cursed Shore all have really nice exotic armor for sale with Power/Vit/Toughness stats for 42,000 karma each. By the time I was running dungeons, I already had enough Karma saved up to buy the chest and leggings, so that was a huge boon that alone has boosted me to just a hair under 17000 base HP.
You can't buy all the Power/Vit/Toughness pieces from the same Karma vendor. I got the leggings from one of the Karma vendors at the Cathedral of Glorious Victory in Cursed Shore. I got the chestpiece from one of the Karma vendors at the Cathedral of Verdance in Cursed Shore (and saw most of the other pieces there on that vendor too). I haven't yet checked out the Karma vendor at Cathedral of Eternal Radiance in Malchor's Leap yet, so not sure if there are any Power/Vit/Toughness pieces there or not. There are other Karma vendors down there too, such as one at the Narthex in Cursed Shore.
Hope that helps anyone else sweating where/how to get the exo armor you recommend for the base amount of HP you recommend.
you can only get 5 piece of karma gear that have toughness power vit you have to get the helm from HoTW or AC