Look at the sentence again:

сам вырастил, сам переработал, сам продал - Note the verbs, they're past tense first/third person singular. That's why you can use сам there.

самому вырастить - here the verb is in infinitive, therefore it's impersonal so you have to add this person there, by making сам dative. Think of it as "the action that the verb conveys goes to someone", so it has to be dative.

Same with нужны, it's impersonal as well

мне самому нужны вещи...

That's just grammar, don't worry about this too much.