I initially liked a non Muslim boy through non halal means and I since then have repented and continue to do so, as ashamed as I am to admit it, we would consume alcohol and commit zina

I for the almost the last year have been repenting and trying to ask for forgiveness however I am stuck with some dilemma

The boy and I 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 and alcohol? Would it have an effect on future children? Is this marriage permissible?

Yes the marriage would be valid. If a person was married and committed adultery with another person, they would not be able to marry the person they committed adultery with. However if they were not married and committed zina then they can get married. You have to continue doing istighfar and he needs to do istighfar as well.