I don't think there is a torque spec for the spindles--just tighten them so they don't have any play.
The Ingersoll OEM belts are 9/16" and I have never heard of any other source for that size. Kevlar power rated belts in 1/2" and 5/8" will work but may need to be a slightly different length since they will sit higher or lower in the groove. Personally, I have had excellent experience with the OEM belts and don't feel there is a meaningful savings by using an after market belt. I don't recall wearing out a single OEM belt but I've replaced a lot of after market belts on equipment I've purchased. The only time I've replaced an OEM belt is when it popped off the deck pulley and got sliced by the blades but that was my fault for not checking the level of the deck. Since leveling the deck a couple of years ago it has been trouble free.
The Ingersoll OEM belts are 9/16" and I have never heard of any other source for that size. Kevlar power rated belts in 1/2" and 5/8" will work but may need to be a slightly different length since they will sit higher or lower in the groove. Personally, I have had excellent experience with the OEM belts and don't feel there is a meaningful savings by using an after market belt. I don't recall wearing out a single OEM belt but I've replaced a lot of after market belts on equipment I've purchased. The only time I've replaced an OEM belt is when it popped off the deck pulley and got sliced by the blades but that was my fault for not checking the level of the deck. Since leveling the deck a couple of years ago it has been trouble free.