Hello, Elle!
If you are known as "Erchie", you would likely spell it so, yes.
Yes, ask the family, I'm sure they will know, or know of, several Erchies!
I enjoy Neil Munro.
He is best known for Para Handy (Peter Macfarlane), but he also wrote about Erchie MacPherson who was a waiter and kirk beadle in Glasgow, and he wrote about Jimmy Swan who was a commercial traveller.
Munro was a good friend of J.M. Barrie and Joseph Conrad.