(1) Xiaofeng's father spent 4320 yuan on furniture, and the price tag was 4800 yuan (4320/0.9 = 4320).

(2) If Xiaofeng's father buys these furniture at one time, he should pay 5920 yuan (2600+4800=7400, 7400X0.8=5920).

(3) In the case of (2), 1480 yuan (7400-5920= 1480) can be saved, and the ratio is 1480/7400=20%.