Just straight Warpriest 20 is best for this, to be honest. Mixing classes, especially non-full BAB classes, mostly just serves to delay your progression down the feat chain.
Greater Weapon of the Chosen is a lot of investment to make, but Warpriest is not a bad way to go.
Your stat bonus from one level of Feral Hunter can be entirely replaced with a +2 Strength Belt, and they don't stack. I don't have a lot of ideas for Lead Blades, except Cracked Vibrant Purple Prism Ioun Stone + wand (2,750). And once you get your strength belt, you can shift your animal focus into Con...you know what, Hunter looks good, even if you do lose a point of BAB.
Have you considered taking levels of a Rage class, for Furious Finish (+Invigorating weapon)? Titan Mauler Barbarian to reduce your oversized weapon penalty, or Abyssal Bloodrager to auto-enlarge from level 4.
Considering that Furious Finish effectively doubles the average damage from your weapon dice, it's hard for me to imagine a serious Vital Strike build that doesn't cycle it.
Two levels of Scarred Rager is the easy way to do this. Because of the Tolerance ability at level 2, a Scarred Rager who rages just long enough to attack is only fatigued until the start of their next turn. This means that you can activate Furious Finish with every single Vital Strike you use. Extra Rage will get you plenty of uses.
Do you have other plans for the build than one high damage attack in rounds with movement? Do you expect to have mythic ranks at some points?
I think a normal war priest is a good way to go all the way. You get bonus feats to get the vital strike like a full bab guy and you get increases damage dice, so you dont need to use a oversized broardsword(but it May still be a good idea) And you get swift action buffs and spells.
I still think vital strike is situational but war priest is not a bad way to go. Talk it over with the GM how he rules impact enchantment and the warpriest increases damage dice interact. And save up for a weapon like that.