My printer recommendation is the Epson WF-2540 printer. This is now connected to the router using a regular ethernet cable or the wifi.
Your father can now print his stuff from the laptop or from his mobile phones (both android and iphone) on top of the wifi network.
I'm not sure if you know, but when you install cyanogenmod (or one of the hundred different ROMS that people are actively developing on xda-developers), you get a Google free operating system. There is NO integration with Google. It is only if you install the "gapps" package, that you get the whole google shebang - play store, services, etc.
As a hacker friendly phone, I can develop on the N5 using Python, Golang, Scala, C#/Mono, QT, etc. - is there a usecase at which the N900 blows this out of the water ?
The only valid point I can think about is the keyboard - yes, it is a paradigm shift. But for daily use, smart keyboards like Swiftkey, Touchpal (pure open source) will serve you very well. For your developer needs, connect a monitor through HDMI/MHL and use a microusb adapter .
You have a first grade terminal emulator, IRC, low power bluetooth, built-in VPN + tethering - I would argue much more suitable for the developer than the venerable N900. Did I mention quad core processor, GPU and 2 GB of RAM with a brilliant display ?
If you want, you can install other OSes on the phone.
The install zip file was just 196 mb.