foodplot tractor
#5

R1 (Ag tires) will provide a better bite no doubt. R4's have a thicker ply rating for punctures and are wider than R1 tires. Guessing you are purchasing this tractor new? If not, you can not just change between the R1 and R4 as they will need different size rims.
#7

It will suprise you how much work can be done with a small tractor