Well, a basic way is to total up the power consumption of all the appliances you need and make it at least 1.25 times.
So fans is 75W x 4, lights is 25W x 6, TV 80W and PC 400W I guess. Totals up to 930W.
And you should have some buffer leftover as you can't operate on peak output. So around 1200W.
2000VA inverter should suit your needs very well.
