Your field labels are displayed in the form and should make it clear what the user is entering. The machine name and whether you reuse fields should be decided by your naming convention.
By default, the machine name is created from the field label. This will get the job done, but without planning, your naming can get all over the place and be difficult to reference in code. You want to be able to see a pattern in the names when you work on the code.
One tricky thing to remember is that machine names are limited to 26 characters, so you will have to be very careful or you will run out of space. Pick a short prefix to give you more space for the name.
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