On drawing style: you fail. Lots of manga have wildly different art styles, it is impossible to describe an art style that is common to all manga.
On plot similarities: you fail. There is no master template plot that all manga follow.
On quality: you seriously fail. There are some brilliant manga out there, but there'd plenty of utter shit. Lurk on /a/ for a bit and you'll see someone poking holes in one sooner or later.
On nationality: well, this is a slightly tricky one. By the Japanese definition, manga refers to all comics. By Western definition, manga refers to comics originating from Japan.
This idea some people have that Westerners can make a manga by emulating some perceived stereotypes of the media is weeaboo faggotry at its worst.