Bulding a physical calculator from scratch

A good beginners platform would be arduino. For language you will need to know some C / C++

Hardware you could either use a plastic matrix keyboard or for more of a challenge use some micro switches on perfboard

Good places to purchase from are farnell, digikey, arrow, or RS to name a few (just google them they should be top of the results) Ebay and amazon can be good for small quantities

Here is an example project you could draw inspiration from Arduino Calculator

Maybe you can also try MicroPython, there are mutiple microcontrollers/development boards supported, and you should feel right at home with your previous knowledge of snake power.

That said, Arduino's probably a better choice, with all the libraries and tutorials and projects available. Also, it's using C/C++ with some baked-in libraries, which means you can still gain some reusable knowledge shall you go deeper in the field (most of which still runs on C and sometimes a touch of C++)