Ahsan Allahu ilaikum: can one say the following? 1. If Allah wills and we do such and such 2. If such n such happens in Sha Allah 3. In Sha Allah, if I can..... 4. Etc im confused becus i think theres a hadith on prohibition on one of these but dont know which exactly

I do not think that you have given the right examples. I think what you mean is, "Whatever Allah wills and you will." This is forbidden. As for what you have said—if Allah wills and so-and-so happens—there is nothing wrong in this or the other examples that you have given. BarakAllahu feek.