3 or 5 gallon barrel?

Hello,

My wife surpised me with a medium char American oak barrel for my birthday. Unfortunately, she accidentally ordered a 1 liter barrel (great for whiskey around our dog's neck but not so much for aging beer). Thankfully, she has asked me to pick another one out. She meant to get a 3 gallon, but now I am debating 3 vs 5 (anything larger is seems to be out of price range). My thinking is I will use it to age a couple of big stouts and when the oakiness starts to go, use it for sours and dedicate it for that for the rest of its days.

Should I go with a 3 or 5 gallon? If I fall shy of 5 gallons, will head space be detrimental?

Should I get the version that is airlock capable or not?

Thanks for any input.

the smaller the barrel, the higher the surface area and thus more oak & angels share quicker. you want as big as you can handle

head space is very detrimental

Thanks dcp27.

I would also buy a used one if you can. New oak would be overpowering in any beer. Used liquor barrels show up in the vendors showcase every so often.