I initially liked a non Muslim boy through non halal means and since then have repented and continue to do so. We wish to get married and he has researched Islam on his own and wishes to convert. Would our marriage be valid if we repent for our earlier mistakes of zina. Would it have an effect on future children? Is this marriage permissible?

If he truly embraces Islam, and you repent to God Almighty of the great immorality you have committed, then God is Forgiving, and you can marry.