Dave, I remember every one of them all very well indeed :). I still have my ZX81 packed away in a box somewhere.
You will be pleased to know that the Arduino environment hides a lot of the complexity of C, and it's a heck of a lot easier then z80 assembler so you shouldn't have too much trouble. And there are lots of examples for the kind of thing you are doing. And many people here that are knowledgeable and glad to help.