1) No, they do not sound the same. The spanish "r" sound is very difficult for chinese people (AS MANY OF YOUR SOUNDS ARE DIFFICULT FOR US:) ) and is usually replaced for the "L" sound, but for us, spanish, both letters are pronounced clearly different. Before you learn to correctly pronounce the "r" sound, you should use the pronoun in such sentences, to avoid misunderstanding: Tú eres un hombre" "Él es un hombre".
2)Most times we can omit the pronoun, because we can distinguish the subject thanks to the conjugation of the verb. In this case, you can omit the pronoun.
3)No, you cannot say "tú es", just "tú eres". Usted corresponds to the chinese "nín", and has a special conjugation. Whenever you use Usted, you must conjugate as if it were the third person, but if fact, it is the second one. So, always eres for tú and es for Usted.