All depend on how you want to do the system and the arduino that you want to select(or other MCU).
In this case something like the arduino or even a esp8266 module can be suitable for you because you don't need to have a hardware to program the MCU, all is included in the board.
The second aspect that I saw is related to the arduino that you are planning to use because the arduinos like Uno and Nano only support Interrupts on two pins (I only have the Nano) but other boards support more, as you want to control 4 machines one arduino like Mega, Micro, Leonardo, Zero, Due need to be used.
I was looking on the Datasheets of some of the PICs MCUs that I have and the 16F690 support upto 10 external interrupts, but as I commented before you need at least a pickit2/pickit3 to burn the firmware.
Another aspect is the communication channel with the host PC, how fast it need to be depend on the stroke rate.
Also if you want to have all in the same board, you can consider the Arduino Yun or the Raspberry Pi Zero (5USD). The first include an arduino plus an AR9331 Wifi SoC. The AR9331 include OpenWRT Linux and have python preinstalled, then I can develop one software for the arduino that save in a DB the strokes (SQLite3) and other that use the bottle framework and some other libraries to create a Web (with python) that let you query to the DB, show the result in a webbrowser and export to CSV,EXCEL or other formats. The second one is just a Raspberry Pi that use Linux too.