Is it obligatory to draw up a marriage contract, and is the marriage valid, and does the wife need a guardian, knowing that she embraced Islam after the marriage, and the marriage took place with two witnesses, a dowry, and the father's consent, without drawing up a contract?

If the marriage was contracted with your father's consent and the testimony of two witnesses, it is a valid marriage. The absence of a written marriage contract or the registration of the dowry does not invalidate it. However, it is advisable to write the contract to safeguard rights. Since the marriage took place before your conversion to Islam, your father was your guardian (wali). The contract can be rewritten for documentation purposes. As for now, your father cannot be your guardian due to the difference in religion, but you do not need a guardian for the validity of the previous contract.