Hello,
I've posted my preliminary bid for the project, but I'd like to know much more details before we start and look on what you have. Before that, it's impossible estimate possible needed time/efforts.
It looks you have another, large project on the VB6 and would like integrate GUI/form developed on the C? Again, what kind of C, is it MS C (+MFC) or Qt or something else?
Too many things depend on details.
I hope you understand.
Thanks
Igor