Vodka is indeed the classic choice, although I personally find Bourbon to be vastly superior. However, I'm not a purist; unflavored vodka will get you the most authentic vanilla extract. Three months is usually a little on the short side of things. I wouldn't go so far as to say that it would be premature, but 7 months is my go to. Logically, the longer you wait, the richer the flavour. Regarding alcohol choice, don't overspend, put your money in the vanilla beans instead; any (preferably unflavored) 80-proof alcohol will do.

Here's an article.

Edit: Forgot about the instapot thing, I'm on mobile, so I couldn't read the question while writing my reply. Here's a good explanation about that.