I'm making a level 2 Elven Witch for an upcoming game and I'll have normal WBL, which I believe is 1000gp.
My focus is definitely going to be on debuffing and finishing with the Sleep Hex, so I obviously don't need to invest in armor and certainly not much in weapons.
So, uh, what do I buy? I want to know more spells, but can I buy new spells the way a wizard can? Is there a standard price for learning from someone else's familiar the way there is for learning from someone's spellbook?
Is it a good idea to buy a bunch of scrolls to feed to my familiar? Perhaps I should buy level 2 or even 3 scrolls to make sure I get more spells that I want later?
Is there some mundane equipment I'm forgetting? Masterwork Silken Ceremonial Armor as a back up behind my Mage Armor?
I'm generally very good with mechanics and character builds, but this is my first Witch (and prepared caster in general, actually), and I'm not big on gear, as the games I run are very low wealth.
If your GM allows Eastern Armor you have two sets of "armor" that you can wear. My witch is wearing Haramaki which gives a +1 AC bonus with 0% SF and 0 ACP. There is the Silken Ceremonial armor, which is the exact same stats as the Haramaki, but costs 27gp more. Best bet for making some quick gold at lower levels is the Scribe Scroll feat. A scroll of Mage Armor can net you about 25gp per scroll and you are limited by how many times you can cast the spell per day. not a bad racket for a lvl 2 witch.
As far as I know there's no formal rules for paying another witch in order to learn spells from their familiar. Assuming that you have access to a witch that has the right spells, I'd probably just use the same rules as are already available for the wizard.
If a witch is not available, you can buy scrolls and feed them to your familiar as outlined in the witch class description under the familiar. The exact rules can be a little tricky to find, there's a link to the ruling here. Ctrl+F and "Adding spells to a familiar" should find you the relevant passages.
Like you mentioned earlier, Masterwork Silken Armor is not a bad option. Your AC will probably struggle, but every bit helps.
Overall you'll want to be spending money on the same items that most other spellcasters want - metamagic rods are useful, scrolls of the spells that you never realize you need till you need them, you can never have too many pearls of power, and so on.
If you're going the Cackle route keep in mind that you won't be very mobile, so anything that lets you move around on the battlefield with a swift action is very attractive.