I hear ya but I'd "take the chance" April would find a very good ST coach -- and like Marv, he'll have great input on how it's run. Besides, chances are April moves on soon anyway for more money and responsibility.
As for no HC experience, there is no doubt Bills' fans are a bit gun shy by now. But, that experience is certainly no guarantee for success, and just as important, not necessarily a indicator for failure: M. Lewis, J. Fox, etc.