1) Depends on the Amp rating on your breakers...most are 15A, so you dont want to push them more than 1500 or so so 900 is more than fine
2/3/4) Yes these are server rated PSUs designed to be run at max load 24/7...you can easily run 4 Apollos @ 800 watts on it
5)Just make sure you buy two pcie cables per Apollo and plug both of them in running turbo

S1)Because the input socket is standard for all PSUs (C14) but people have diffrent plugs around the world so its easier to just buy the PSU and buy your own power cable locally
S2)US shipments will have power cord for sure, ill probably stock one or two major Euro cord types (UK/Eurozone)