I switched from Ubuntu to Fedora about a year ago and am quite happy with it.

Well 1 depends on Wayland actually detecting your external monitor, I normally end up having to drop back to X to get it to detect my secondary 28" 4K monitor :-(

I couldn't figure out where I can change the different scaling for the external monitor on my fedora 25. My 1080p external monitor just looked huge comparing to my dell xps 13 hidpi display.

It requires Wayland features that are used by GNOME 3.24 (so F26).

really, there's a native multitouch support for touchpads? do you have more info about that?

Yes there is native 4 finger swipes to change desktop on Wayland. And I wrote an extension to add 3 finger gesture support for an action of your choice. Check it out here: https://github.com/mpiannucci/GnomeExtendedGestures

I can't find much information, but things like scrolling, switching work spaces etc. worked out of the box for me when I was testing Fedora 25 a month or so ago.

Two-finger scrolling works really well on Fedora with Wayland, in fact at some point it appears to have become default behavior (at least on my machine running the latest version).

Fedora uses libinput. Of course, it is not without issues from those, who would like to tweak every little setting. Libinput is designed to be as automatic and configuration-less as possible.