I've got a porter that I'm going to keep in primary for 3 weeks. Once that's done is it ok to rack to keg and add bourbon/vanilla. Then put 12 psi on it while its in the fridge at 40 degrees for 3 weeks? Or should I secondary with the bourbon/vanilla before kegging it?
Are you soaking the vanilla beans in the bourbon first, or is it vanilla extract, and bourbon you're using. You usually add the beans to the secondary. Taste test as it secondaries, then rack it off the beans when the right flavor profile is achieved. You then add bourbon to your keg or bottling bucket to taste.
Pure Vanilla extract you could probably just put it right into the keg/bucket to taste
Careful with the bourbon. I recently made an IPA with bourbon and oak chips. It is very easy to go overboard with the bourbon. My last experience was that a little goes a long ways. I added waaaaay too much.
If you're doing the recipe I think you are (Denny Conn's), then you want about 8oz of bourbon. I threw the bourbon, two vanilla beans, and oak chips in a carboy, and racked on top of them for two weeks. Turned out great!