If you are doing mostly part clean up and standard fab work, you will get much more use out of a flat platen than a wheel setup.
You probably don't even need the VFD. That's really most helpful for fine-grit finishing. You could just use the pulley setup.
I would then use the money saved to get a horizontal grinder instead and use the small wheels there.
If you decide to get into knives, you can start with flat grinds....then if you decide you like it, get a 10" contact wheel.
1.5 HP or 2 HP is plenty.
You only need a spare tool arm if you have something to put on it.
I can't answer about whether or not you'll need the contact wheel on the flat platen....that's something you'll have to figure out when you start using it. I had one and didn't like it, nor use it much. If you get one, you only need 1.
Best of luck!
Dan