what would be the best size fuel cell for my truck and also what fuel pump would work best or could the stock pump work?
12 gallon RCI or Summit, and I've seen plenty of people modify the in tank pump assembly with no problem. You could get fancy and get an aluminum tank.
I run a custom made stainless 12.5 gal ( same as stock) , used stock flanges & filler neck. Range is around 300 + miles. Have Vemon pump ( 10-20% more flow), & a AutoMeter sender!