I'll report back, but my research seemed to indicate 2 beans and 2 cin sticks in... also had lactose though. I've had 2 beans in a milkshake IPA and it was too much, but i'm thinking you may need a bit more for a stout (1.080sg)
depends where yo are using it. 1tsp cinnamon in boil is noticable 1 vanilla bean soaked in vodka for a few weeks is often enough in the keg.
I find using tinctures is an easier way to go post boil. I put 2 tsp cinnamon in a half pint mason jar filled with vodka. i let that soak shaking occasionally for a couple weeks and use it it titrate a sample of the beer then I scale it up for the batch. generally 1 tbs of high quality vanilla extract per 5 gallons or 1-2 beans soaked in just enough vodka to cover the beans is enough. If you have a tj maxx, home goods or marshalls in your area they often have Massey vanilla for $8 a bottle its $20+ at williams and sonoma and works great at 1 tbs per 5g.