A 1000Watts UPS will be enough for your system. It requires two batteries only and can give you 1 to 1-30 hr backup. Use 120 to 150 amp of battery. If you move for dry batteries that are long life and provide you more time. My UPS has no usb interface but an automatic beep system is there which starts beeping when 5 min backup time remains (for you saving documents and proper shutdown).
Rates of UPS
1000 Watts UPS 11,000/-
1000 Watts UPS with Best parts 14,000/
Rates of Batteries
Liquid 120 Amp 5500/- Local (Some venders are selling it as Imported) for 1 hr backup
Liquid 150 Amp 7500/- Local (Some venders are selling it as Imported) for 1 hr backup
Liquid 150 Amp 10,000/- Imported 100% Guaranteed full Amp (Gives you full backup) for 1 to 2 hr backup
Dry 100 Amp 9000/- without warranty and 18,000/- with warranty for 1 hr backup
Dry 120 Amp 10,000/- without warranty and 20,000/- with warranty for 1 to 1.25 hr backup
Dry 150 Amp 18,000/- without warranty and 36,000/- with warranty for 1 to 2.5 hr backup
Two dry batteries means 3hr backup time.
Feel free to contact me any time.
One more thing my UPS is repairable and have 10 months full warranty and the UPS like apc or systek costs too much for repairing sometimes non repairable.