Does Ban feel any pain? Everytime he receive fatal blows his reaction looks like he’s in pain but when he fought the needle guy of the six knights of black even having a needle throughout his body he still able to defeat his enemy by hugging it to death disregarding the needles throughout his body.

Does the fountain of youth had the ability to make the wielder immune to pain?
Yes, he feels pain, but most of the time he tends to enjoy it especially when he fights the captain. See season 2 episode 2 which was named "Futari no Ken'ka Matsuri".