If building a grinder from the ground up:
A removable tooling arm style is the way to go. These are three wheel type grinders ( four with a flat platen). 1.5" or 2" arms and box tubes will be rock solid.
A second tooling socket below the main arm socket (box) for jigs and work arms. This is a really good feature.
A flat platen the rotates so you can use the 4-6" wheel on the top, the flat part, or the 2" wheel on the bottom.
A contact wheel arm for larger wheels. You can make this with a two wheel rotating end so you can quickly switch from a 6" to a 12" (eg) contact wheel .
A small wheel arm for wheels between .5" and 1.5".
A VFD motor of 1.5HP to 2HP. 1HP will work, but larger will be far more useful down the road.
A foot switch and a remote speed pot are super useful and much safer.
Using gas cylinders or pneumatic cylinders for the belt tensioner. Pneumatic cylinders allow quick increases and decreases in tension.
Making the whole assembly so it can flip on its side and be used as a horizontal grinder.
Overbuild everything. 1/4" plate is a minimum, 1/2" isn't too thick for main components.
Weld everything that isn't adjustable.
Paint the whole assembly except sliding components. Powder coating is even better, and really professional looking.
Make a tooling "tree" type stand with sockets for the arms, and pegs for wheels and other things. Making it with a rotating base will allow more tooling in the same space. Put a box on the top for knobs, wrenches,and tools
Other items, like radiused platens and a water cooled platen mounts are great for those doing high end and production work, but not so much needed by the hobby level maker.
A very good second build is a VFD controlled disc grinder. That would be perfect for the 1HPmotor. This is a very simple build and really useful in the shop. Nathan makes superb precision discs. Wayne Coe makes a quick change disk system.