Well, I've started taking a crack at it, and I think it's going tolerably well for one evening's work so far. I've attached my file in case anyone's interested. Todo list:
[X] Skills
[X] Weapon and Armor proficiencies
[ ] Athame Bond
[@] Patron Spells
[@] Battle Tactics
[@] Bonus Feats
[@] Hexes
[@] Spellcasting
[ ] Athame Training
[@] Major Hex
[ ] Athame Mastery
X = done
@ = in progress
blank = not started
Witch Skills These work. As you suggested, Aaron, I just made three selectors that offer the skills from the Witch list that do not also appear on the Fighter list. It's annoying that the Knowledge skills don't show up in the selector until you've added them as picks on the Skills tab, though.
Patron Spells: I got it to let me pick a patron. It isn't actually adding the spells to the spells known list, though -- I'm guessing I need to add an eval script to do that.
Battle Tactics: is working okay. I've got an eval script in there which correctly calculates how large the bonus is and assembles a string to tell you what it is. For example, "Battle Tactics (+3, 6/day)" at level 11 with 16 INT. Unfortunately the live name is not getting updated. It's stuck as "Battle Tactics (6/day)", lacking the +3 bit. I'm not sure why not. Timing issue? The bit that's supposed to update the sbName is running at Render 10000.
Bonus Feats: working fine, with one issue, which is that "Extra Hex" complains that the PC doesn't have the hex class feature. Which it actually does. It looks like the validator for that feat was written to test a bunch of specific classes/archetypes, but there's no generalized HasAbility.witchHexes or anything. I suppose I could write a custom copy of Extra Hex specific to Witch Blade and include that on the bonus feat list. That'd probably do the trick.
The original text didn't specify whether or not the class counts as fighter levels for purposes of feat pre-reqs. I made an executive decision and went with "yes, plus it counts as witch in case that ever matters."
Hexes: you can pick hexes just fine, and they work normally. Major Hexes complain about the PC not having 10 Witch levels. The validation seems to tie into a field reqLevWit with a value of 10 on the custom ability. Maybe I need to write an eval script to assign that field to the hero with an appropriate value at level 11? Not sure.
The other issue with hexes is that the "Allow Custom Abilities" inherits ALL witch hexes. I'd prefer to exclude Grand Hexes -- since the PC will never qualify for them, they may as well not be on the list. Not sure how to do that. Just specifying the class to inherit abilities from is super-easy, but also pretty all-or-nothing. I really hope there's a better alternative than re-implementing all of the Witch hexes as Witch Blade custom abilities, because that would be ... tiresome.
Spells: I've entered the spellcasting progression and characteristics. It lets the PC learn and prep witch spells, the save DCs are correct, and so forth. The one downside is that it's showing the whole witch spell list, including cantrips and level 5+ spells which this class doesn't have access to. I set the lowest and highest spell levels to 1 and 4, but I guess it doesn't trim the list using those?
So that's all for one evening. Decent progress, I think, though honestly, this is the easy stuff. I'm dreading Athame Bond.