Re Mechanical keyboards - I still have some Apple II Extended Keyboards which can be converted from ADB (Apple Desktop Bus) to USB via various internet hacks or by using a Griffin iMate adapter (expensive but still available on eBay or Amazon).

For PC users, mechanical keyboards seem to be produced largely for gaming purposes and seem to be available for both PS2 and USB connectivity, from reasonably priced to megabucks. If you find an old PS2 keyboard, adapters for USB seem to be very cheap.

This article was very interesting.

https://www.theguardian.com/technology/askjack/2015/apr/02/laptops-suitable-for-high-speed-typists

I am typing this on a MacBook, but if I had large quantities of text to input, I would look to connecting up one of my old keyboards in preference to the laptop keyboard.

Ross