Hi Key,
With an HD touch, you can use fingers as well as the Pen.
If it’s mixing you want to accomplish with this portable setup, you could well be OK with a wacom intuous and your wife’s notebook (I reckon it’d be enough if you don’t plan on using kontakt and large strings setups).
If you want to write music with Nuendo, you’ll be limited to pick notes and symboles and place them on the staff by hand.
With a tablet, it is anyway faster than a mouse… You hoover on the wacom and pick to grab like with a mouse click.
I used this setup for years.
The Cintiq is a Big step above but at a price. The added benefit of a screen below your hand is nice and gives you a surface like experience with an extra screen… However as a pointing device, an intuous is more than enough and only need a couple of hours of practice before being fluent with it.
https://plus.google.com/+wacom/posts/awpJkqGM7oP
If you want to write notation like you’d do with a pen, you’ll need Staffpad and a Surface 4.
So it all depends on what you want to accomplish.
Mixing and using Nuendo notation system, go with your notebook and intuous wacom.
More cash, go for a cintiq.
Want to handwrite music, spend cash and get a super compact tool, surface 4 and Staffpad.
All of the above and more cash, go Surface book.
Hope this helps.