I would aim for a small group of friends, when I started GMing everything I read said never do more then 4 starting out because it just becomes a nightmare to manage and make fun for everyone if you are not prepared.
Other two questions are really up to the person running the adventure and the people in the group, if the players are less into the role playing parts of it and more just want to get into the combat then you probably want a higher number then a group that wants to try and talk their way or stealth their way through most problems.
Maps can make for great world building material though!