Since you have the chains already, I would get the spacers. Chains will make the most difference. I would only chain the rear and let the front slip to relieve binding. You can chain only the front if you're careful with direction changes and let the rears slip to relieve binding. But if you chain both, you can get binding that is damaging to the drivetrain.
I have used front chains only because I had them already from an old truck and I didn't have the clearance in the rear. I never had any problems from using them and the tractor was unstoppable with them on. However, the v-bars took chunks out of my concrete floor in the shed so I stopped using them.
Then I tried grooving all of my tires. It made a tremendous difference for me, even on solid ice. I've never used chains since. Do not get me wrong, v-bar chains are more effective than grooving your tires, there is no comparison. But grooving your tires and then adding weight does a lot. I'd say that a balanced 2WD tractor with grooved R-4 tires can push about as much in packed snow and ice as a 4wd tractor stock R-4 tires. So it maybe doubles your traction. V-bar chains will make your traction go up 10x and thus the fear of breaking driveline parts if chaining all 4 especially with v-bar chains.