I've brewed this base beer several times with different additions. In the pictures you can see the original, chocolate-vanilla version, which was my very first stout, and one of my best recipes ever.
For vanilla version: when fermentation starts soak at least 2 vanilla beans in vodka until secondary (2 weeks). Be sure to scrape out all the vanilla, chop up the bean to small pieces as well and put everything into a small jar. Shake it up every now and then. Dump all into secondary and transfer the beer on top.
This beer was amazing from the first day, but also aged really well. At the second year mark when I opened the last bottle the vanilla has disappeared, but the beer was truly amazing.
I also highly recommend you try this with medium toasted american oak chips!