With the backhoe removed most of the time, you will definitely need counter weight for the FEL. In most cases, both tire weights AND fluid filling the tires is called for in the FEL or tractor manual. You will have to look at your manuals if you have them and see what is called for. Normally only the rear tires are filled.
On my John Deere 4410, the rear tires are filled with Rim Guard. About 50 gallons per tire. I still reguire a rear counter weight such as a box blade or bush hog with using the FEL with much weight.
Typically, filling the rear tires with fluid and a box blade or other heavy impliment is usually enough to cover most jobs but for heavy jobs may require more counter weight.
You will have to experiment with weight combinations to see what works best. Just remember, it is better to have more counter weight than you need than not enough.