Shelley was a key member of a close circle of visionary poets and writers that included Lord Byron; Leigh Hunt; Thomas Love Peacock; and his own second wife, Mary Shelley, the author of Frankenstein.
If the 900 watts means the input power, then 1000 w inverter would be ok. If the microwave produces 900 w of cooking power, you will need a bit more, maybe 1200-1400 w if you don't know what the input power rating of the microwave is.
All the other appliances together require about 300 Watts. So the minimum size inverter for our example is about 1500 Watts. If you plan to run the microwave and other high power items from the generator instead of the inverter you can use a smaller inverter.