When calculating load, make sure to factor in any start-up transients which may occur, especially in motor driven devices. These can often be close to 10 times the steady sate load. Things like air conditioners, well pumps, refrigerators, boilers, furnaces, and TV sets tend to have relatively high start-up demands.
I run a 5.5 KVA (10 Kva surge) sine wave inverter, which is fed from 24 2 volt, 660 Ah cells, set up as a 48 volt bank. the inverter has a built-in charger and transfer switch. Everything is fully automatic. The transfer switch works so well, I can't even tell if the power goes out (unless I try running the clothes washer or dishwasher, which I chose not to conenct to the inverter)!
I realize you're looking for something small, but be sure to factor in EVERYTHING you could possibly want to run during a power outage before buying equipment, and then oversize a little for start-up surges. It's always cheaper to buy the right things once than to start small and then have to scrap everything and buy bigger capacity equipment.
73, de Tom, KA1MDAwww.ka1mda.org