I prefer Rohan to Rowan but both are fine. I've known three Rohans though and the most recent one (I work in a school) was constantly being called Rowan by others. It probably didnt help there was a Rowan in the year group too, but I know it did his head in!
Jaspers in my experience have all been dogs or dickheads (I've never worked with one, only known adults)
Louis I really like assuming it's a Louie pronunciation. (edit- I'd still put it above Jasper it was a Lewis though!)