We bought two to get the one we wanted because we couldn't afford the one when wanted when we wanted it. Or, more aptly, we couldn't justify affording the one we wanted. If you are confident, and liquid, I would go for it.

If I were buying a single that I would want to ride regularly, I certainly wouldn't buy "less" then my tandem. The reverse would be the same for you. Given your level of riding and current stable, I doubt you would be happy with the starter bike most of us bought first.

Good luck - nice choice of first tandems. I am jealous.