I live in Northwestern Florida and I use water in my 990's tires. Most people around here have there tires filled with water, heck my dealer did it free when I bought the tractor without me even telling him to.
Easy to do. On larger tractors, there are usually two types of wheels. One is a steel wheel like these tractors do. The other is a cast wheel. You can add weights to both. I use both liquid and weights on my 5000 series tractor.
Yep, go for 125 lbs/ PTO hp as he said. If 2wd, put 70% on rears, if 4wd, use 60%. You may need more on the rear to offset the FEL. Your operator manual covers it too. For these type applications, you can go above the 125 lbs figure.