I'm playing a Warpriest of Erastil (heavy pick and shield, plant and law domains) in Reign of Winter. We are only at second level now, and I started with Improved Initiative. I'm planning to take Quicken Blessing and Blind-Fight but other than those I just have the standard martial feats planned (power attack, weapon focus, weapon specialization, etc).
What other feats could be useful?
Personally not a big fan of Weapon Specialization and it's ilk, particularly since you already have so much scaling damage all over your kit. (Don't you already have Weapon Focus, though?)
Anyway, I actually vouch for Toughness for Warpriests.
Is step up really usable with how many swift actions I'll be burning just on class features?
I didn't realize hp would be so important, I currently have 14 con and was planning to put my first two attribute upgrades into it as well. I already have two FC points in 1/6 combat feat and was going to go for two of them. Trading six HP for a feat when I'm using a feat on toughness kind of lowers its value.
Should I stop at one combat feat and start putting my FC in HP or get two as planned and hope Toughness will balance it out?
Trading 6 x FCBs to get a feat such as Toughness is actually pretty good economy at higher levels, because as soon as you hit 7th level, it's already become more valuable than 6 FCBs directed towards HP.
Having said that, with 16 CON, you're doing pretty well as it is. I'm not sure I'd recommend Toughness in that case, and would also probably suggest your level increases to statistics at 4th and 8th be used for something like Strength instead of Constitution.
Either way, I definitely wouldn't recommend both Toughness AND bumping Constitution to 18 that way, as you'd effectively be sinking too many of your limited resources into the HP bucket (which means you're correspondingly neglecting something else).
As I try to remind myself -- HP is only one of various aspects of a chgaracter's defences. Saving throws are at least equally important, and possibly more important at higher levels. AC and other ways of avoiding being hit are valuable, as well, of course, and I especially like working in miss chance, which can often do more for defence than a corresponding investment in AC (especially once you've hit the "low hanging fruit" of AC boosts, like basic armor enchantments, rings of protection and amulets of natural armor).
Apologizes, I actually have 14 con. I edited my comment.
Plan I have currently worked up, including base feats, warpriest bonus feats, and 2 FC bonus feats:
1: Improved Initative
3: Toughness, Shield Focus
5: Endurance
6: Improved Shield Focus, Shield Specialization
7: Blind-Fight
9: Greater Shield Focus, Weapon Specialization
11: Quicken Blessing
12: Greater Weapon Specialization, Greater Shield Specialization
13: Improved Critical
15: Critical Focus, Critical Versatility
16:
17: ? No idea here
Endurance and Blind-Fight are dependent on how the adventure goes. I assume they will be very useful in a snow heavy AP full of fey, but it could change.