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The Iron is the plane blade, make sure it is sharp and properly adjusted.

Starting with real horn, will make your project much easier. It is inexpensive and will cut easily with a coping saw and...

'What is the best cutting guide tool to get this done?"

Eyeball.

A bandsaw and hand plane with a sharp iron, to finish to final thickness. Or as said a sander.

You could use a hand saw with...