Re: have been and has been
The subject is still "Mr. Smith" (note that capitalization is important) so it still takes the singular verb.
The phrases "as well as" or "in addition to" don't change the original sentence into a compound subject. I would also set off the other phrase with commas.
Subject and Verb Agreement | Grammar Rules
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.