When I've had followup questions after an interview I've taken the following approaches:
(This is the one I recommend.) Contact the person who set up the interview and, after thanking this person again, say you have a few followup questions and ask how to proceed. Don't give this person your long list of questions right off; instead describe the areas (business development, technical, workplace, etc). That person might then ask for your specific questions or put you in touch with others who can answer -- perhaps some of the people you've already spoken with.
I've done this for a small, informal company but I don't know how well it would work for a larger one: contact the interviewer who seemed to you to be "most significant" to you (hiring manager, technical lead, etc), thank this person and express your interest in the position, and then ask if that person is able to answer some followup questions. (This assumes you collected people's names during the interview. You did that, right?)
In both cases cast your request not as "I forgot to ask this" (makes you look disorganized) but "I had some additional questions I didn't get a chance to ask". Unless, of course, there were long awkward pauses where they asked you if you had questions and you said no -- in that case this won't work and you'll just have to jump to "I have some additional questions".
Usually my questions have gotten handled in a phone call, though in one case I came back for a meeting. (The need for that had been clear at the end of the first interview, though, so while it was a followup, it wasn't a "thought of it later" followup.)
As an interviewer I have rarely received direct queries from the people I've interviewed, but it does happen.