The only thing that puts me back, is that it seems like there's a good chance that an English speaker would say VIE-la, rhyme Isla - and that brings to mind the word vile. So I'd favor the Wila spelling, for that reason. I like the way it looks. You would probably not care about that association, though. So it's just a data point for you.
Overall I like it. It does sound good with your son's name.
My favorite V_a name is Viveca / Viveka.
- mirfak