Install three to four UPSes that can take the load of two or three PCs each. Not having one centralised UPS saves you trouble if it develops faults. Buying one for each though, may be more expensive. Each UPS must give you 30 to 60 minutes' backup on a full load. Install a good-quality generator that does not output frequency variations or other electrical problems. Run your Pcs, the AC and other electrical fittings through this. Ensure you sign a service agreement that guarantees you a standby unit for the UPSes or the generator in case of failures or repairs. You could configure the UPSes to give you two or more hours of backup, but weigh your annual battery consumption costs.