Again take a look at this in 3D using AutoDesk Fusion 360 Online.
A Raspberry-pi handheld platform with a physical keyboard, Display and Expansion header for add-on baords (Like Ardinuo Shield).
Here we will dicusses what you need to build one. This device is very easy to make, you don't need lots of tools and parts.
No codding skill is needed. just basic stuff like uplaod a code to Ardinuo, little skill in Linux CMD line to install the driver. Little soldering skill that's all.
You need this parts to make one for your self (this are not affiliate links):
I added the build guide in Instructables as it is perfect palce for it: