There are lots of people who have done scrollers (both ways). There is actually an example in the AppGameKit installation (but I don't know if it is included in the demo version). If it is, it is in AGK\Projects\Basic\Examples\Games\SpaceShooter.
There really is no level editor for that kind of game in the paid for AGK. There is something called a Placement Editor, but I've never used it and I don't know if anyone else has.
A vertical scroller is basically a horizontal scroller, but you move things in the Y (up/down) direction instead of the X (left/right) direction.
Cheers,
Ancient Lady
AGK Community Tester and AppGameKit Master