I don't think your concrete blocks will work. First you need solid concrete, not hollow blocks. Second, there is a lot of upward force at times and they could pull the block right out of the ground. They are usable (barely) when bolted to a 4'x4' sheet of 3/4 plywood that you can stand on.
Manual Tire Changer Comparison - Harbor Freight 69686 vs. Northern Tool 13474
Next the mount/demount bar that come with both units is fine for steel rims. If you have aluminum or chrome rims, they are almost guaranteed to scratch them. Save your money and buy a
No-Mar Mount/Demount Bar. The plastic tips
(that have a lifetime guarantee) prevent scratches. (See attachment)
Tire lube is the most important item. Old fashioned Murphy's Oil Soap gel works well and is not expensive.
Last,
watch some of the No-Mar videos on YouTube. Even though you don't have their machine, some of the tips they show for unmounting and mounting tires, especially wide tires, are INVALUABLE ! Their special tools are nice, but you can do the same with small blocks of hardwood (maple or oak).