No no no no.
Don't ever use the eraser tool for that purpose. Photoshop has a wonderful feature called layer masks. They can be applied to any layer you like, and are nondestructive. You can be as fine as you like, yet never, ever harm the underlying image.
I made the following EPS in ten minutes using only the pen tool (I know what I said about EPS, but it's small and maintains paths; perfect to upload here). I brought it into Illustrator, and added a really really simple gradient and stroke just as an example.
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