I know it probably depends on software (I have janome mbx 5) but is there a good method to make a closed freehand shape symmetrical on both sides. Should I digitise one half then mirror copy or is there a simpler method?

It depends on the software.
In 6D i copy, paste and mirror. And then carefully line up the shapes. Not very consumer friendly when drawing or digitising without a picture.

In Embird it can be done with one click of the mouse. It has a number of features that make free hand drawing easier

I do not know your software. Are there any hints/instructions in the uaer manual?

with pe design I do it your way, or do the lot , save it import on top of original and flip then alter one side to match, probably takes longer than the other way...wendy