With the rule of 1 to 2 pounds of LR per gallon, you can use between 100 and 200 pounds of LR in your tank. The higher amount is better, if you use it as filtration.
Personal taste will dictate the exact amount.
With the rio 400, that's about 1.5 turnover per hour. You could use a bit more, especially if you use only LR as filtration.