As there are currently no touch display panels available for the FW13, the best you could do is find a portable touch screen that fits within the display panel dimensions, somehow secure it there (either some redneck engineering or actually custom CNC/3d Print parts), and then use one of the expansion slots and a bit of custom wiring for the USB C connection.
And no matter what you do, it's probably gonna look like a prototype/engineering sample at best....
If you don't want that, there will hopefully™ be a touch option in the future, so you could always wait for that; either buy the laptop now and hope to be able to upgrade later, or buy if/when there's a touch option.
The nominal mAh of the 55Wh battery is 3572mAh
HOWEVER that is at 15.4V, while the Powerbank you linked is 20000mAh at 3.7V
So I'd actually recommend doing this the other way around, calculating the Wh of the Powerbank, because Wh is an actual representation of Energy stored inside the Battery, while mAh is only telling you half the story.
And multiplying 20Ah with 3.7V, we get 74 Wh, so that Powerbank is gonna charge the FW 13 about 1.3 times.
Given average battery life reports between 8-12 hours, that should give you between 18 and 27 hours of non-stop use (Laptop Battery + Powerbank),
I'd stick with the 18h estimate, both just to be sure and to account for Windows (assuming you're using it) thinking "Ohh look I'm plugged in so I can use even more power now to run random background tasks", but 18h of run time should still suffice for most if not all situations.