Start a discussion at http://www.greenfoot.org/topics , with some details (ideas, problems, design, etc. ) - then I or somebody can assist you.

A single UserInfo Object holds the 5 Strings, 10 ints, etc. There is storage of a UserInfo for each User, each holding their own values.

UserInfo.getMyInfo() returns the UserInfo associated with your user logged into the site. Look into using UserInfo.getTop(int) and UserInfo.getNearby(int) to get lists of the UserInfos

Flight controls are not exactly straightforward (it's a bit of skill to turn around, besides just bumping against the sides of the screen). Read the controls carefully and practice in flight training. Once you learn how to fly, the game becomes a lot easier.