"I am fairly new to tractors and would like to know the pros and
cons to a heavier tractor."
- heavier tractor will push and pull more before slipping, will be more stable carrying a given load, may or may not compact your yard more depending on tire size.
"Also, if someone could comment on the difference in tires.
Most of my work is hauling material, and firewood and general use around
the yard."
- Turfs are best for keeping the yard nice. That being said, many use industrials on the yard including me. But I don't go on it when it is wet (and wouldn't with Turfs either).
"Should also ask if the JD 3520 is a good model to consider. Have not owned
a JD utility tractor."
- no idea
"The JD also has rear wheel weights installed. Good idea to keep these on?"
- I would keep them on. Extra weight in the back probably is good for stability and traction and usually has no detrimental effect on the lawn because it is the front tires that tend to have he most ground pressure because they are smaller and the loader sits way out front.