What size microwave....that will be the big draw!
You really need to have the numbers of the things you want to run, in order to calculate the inverter size.
I agree with Brett....add an additional 20% to whatever you calculate, you'll be glad you did.
The inverter size won't matter much, if you don't have enough battery power to operate the things you want.
And, consider how many days you are planning to boondock? Will you be using a generator to recharge the batteries? Can you use the generator to make the coffee in the morning, and the microwave as needed? This would take the load off the batteries and the Inverter needs.
Good luck:)