Looking for a game to get my feet wet.

Welcome aboard. We just started the game, so you picked a good spot to jump in as far as I can tell.

Good to know. I think I'll go ahead and try a wizard.

Wizards have a bit of a "hidden advantage" in this game. When finding spell scrolls, if it's on the list of the Mage, he can read it to figure out which spell it is without needing any identify spells or the innate analyze magic ability of Mages. Since Wizards dips into spells which are also on the Healer's and Sorcerer's lists (much more so than the Healer or Sorcerer dips into each other's spell lists), he can make a good identifier of scrolls for the party.

Since Knife is a Sorcerer, do we need a Wizard as well? Maybe I should go healer?

Do not think of DS4 Wizards/Sorcerers in terms of D&D. Healers are protectors and healers with some utility spells, Sorcerers are mainly damage dealers. Wizards dips in both (to various degrees: for example sorcerers are better with fire spells than wizards, but wizards are better with ice spells) but also have a lot of utility spells.

Also keep in mind, like I said earlier, that as a healer, you'll most likely heal others during battle, which can get a bit boring. If you're fine with that, then by all means make a healer, if not well you might want to try something else...