I love my Pi-W.
I got the acrylic case, the badusb usb A(male) port, heat sink, and a short HDMI cable.
It is great for jacking into a TV when on the road and streaming media.
I have a HDMI capture USB dongle for working with it with my laptop a usb 2.0 port is enough power for non intensive applications as is a microUSB phone charger.
As far as gutting the N900 I think using it as an adjunct, maybe doing a bluetooth network and using VNC to get the modern browser into your phone while powered off of a USB power bank is a slightly kludgy but works and is pretty small mobile hack.
I just BT tether a rooted LineageOS phone with the telephony reversibly neutered and browse from that when needed.
This is pretty much what my mobile Pi Zero-W rig looks like though is missing heat sink.