No, this would not be a good solution.
You do not want to connect your Teradak straight to the internet like that, with no way to reach it from your internal network because of your router having a separate network.
Also, this would make your ISP have to supply 2 IPs which most of them don't do or charge you more.
IMHO it is best to stick with your original plan.
Cheers, Hans.
