Smieglitz makes good points.
My 8x10 came with a 4x5 reducing back and two 8x10 Folmer wood filmholders. I've accumulated six more for a total of eight matching holders, the most I've ever taken out is four. I've never enlarged an 8x10, although I plan on building a horizontal enlarger.
For portraits I use a 16 1/2" Artar.