Shouldn't "He is one who wants more." be accepted? In English you actually use "who" when referring to people, whereas "that" is used for animals and objects.
It should definitely be accepted. "who" is better for people although "that" is still acceptable.
I agree with Ben young84
unul = the one
Nope, that's not correct. See my answer to Romanophile's question.
cel / cea / cei / cele = the one I think