Stout Yeast

Pumpkin doesn't impart much flavor to beer. It is a very subtle ingredient. You should be fine with pumpkin puree as I'm not sure what pumpkin extract would do or even what it is. Most pumpkin beers use spices to mimic pumpkin pie flavors. If this is your goal, look into some pumpkin beer recipes that utilize spices and make adjustments to your recipe.

For yeast, wlp001/1056 are a great option for a clean, attenuative yeast and ferments well at higher SG. If you want something a little sweeter, maybe mash higher or choose an english strain. Ferment cooler if you are not looking for those traditional english esters.

 

us-05.
Focus more on your grain bill than the pumpkin. If the beer stands alone, the pumpkin won't ruin it.

 

My favorite dark ale yeast is WY 1028 London Ale. Great attenuation, forgiving over a wide temperature range, minerally profile very complimentary to dark ales.

 

I personally pr4efer the Irish Ale yeast for stouts - don't remember the number for it.
if you're making a starter, then one pack should be plenty. If you're direct pitching, a couple or more, depending on a few things.

 

I always like Nottingham for its wide temp range and ability to reach higher ABV's easily. Slight esters but relatively clean yeast. It's a beast early on so be careful if you go with it.

 

+1 to Nottingham, but just as good but different is Windsor. Windsor gives a more English ale taste, ferments quick and plays well with pumpkin and associated spices. 1 packet per 5 gallons is fine.

 

As @secondbase said, most people are really thinking pumpkin spice (cinnamon, nutmeg, clove, allspice) rather than pumpkin. The pumpkin spice latte didn't have any pumpkin at all until last year. Pumpkin spice

As far as yeast goes - if you want a dry yeast for a creamy stout, I'd recommend Mangrove Jack M15 Empire Ale or S-04 for this application.

Per Mr. Malty you'd need about 1.2-1.5 packs of yeast depending on which one you pick. (Mangrove are 10g, Safale are 11.5g)