Hungryghoast,
Thanks for the thoughtful comments. Taking your two concerns in order:
1. Although at any one given time, the witch will likely have access to many more spell choices than wizards (or other spellcasters), in my view, it doesn't actually have much more versatility. This stems from two reasons. First, wizards (and clerics) can switch spells known easily overnight, while a witch takes a month to switch a spell. As a result, wizards (and clerics) can customize their spells known for an adventure or even mid-adventure quite easily. Second, the witch is drawing from a much small, and less versatile pool of spells. The tradition spells all closely follow a particular theme, while the common spells are actually fairly narrow. To take a simple example, its likely that 10th level wizard is going to have many different combat options, including different types of damage (fire, lightning, cold), summoning, illusions, etc. while a witch is probably only going to be able to do one or two things (e.g. a winter witch can cause cold and piercing damage, an infernal witch can do fire damage or summon demons, a beguiling witch can cause psychic damage or charm effects).
This actually worried me quite a bit, but after playtesting for almost a year, I actually feel pretty confident that in fact witches tend to be much less versatile than wizards or clerics (we don't play with warlocks or sorcerers so I can't compare).
2. Except at the very highest levels, I actually don't think the witch abilities are really all that powerful. The witch's strike is intended to be a last resort if the witch's ordinary cantrips and spells are useless against a creature. Since it requires the witch to be engaged in melee, I would guess it is very rarely used. The witch's armor, as you indicate, is intended to give the witch some AC boost, but it is less powerful than mage armor (although the witch does save a spell slot). The cauldron abilities are mostly useless for adventuring witches (the cost to create potions and poisons is the same as the purchase price, so it is mostly there just to encourage the witch to use potions and poisons). This is really intended for witches as villains. The overland flight is useful, but again it is mostly out of combat. It is certainly less useful than teleport, wind walk and tree stride (and while the witch doesn't need to memorize the spell, again other spellcasters can swap the spell in and out as needed). Similarly, the familiar is mostly like a standard familiar. I feel the tradition abilities are on par with the wizard school abilities and cleric domain abilities (and in some cases were explicitly modeled on these abilities).
At the higher levels, I do think the witch abilities are fairly powerful, although in many cases I would argue that they are less powerful than wizard spells gained at lower level. For example, a 20th level sea tradition witch can use a 9th level slot to call a hurricane once a year. In comparison, an 18th level wizard can cast wish on a daily basis (as long as he casts no other spells the same day).
In any case, the class seems to be working for my group in my campaign. If you do decide to use the class, I'd love to hear your feedback.
BMM