1.) Yes you can do what you describe. Mena661 has a great layout to follow
2.) No, running converter won't hurt anything but if you do forget to turn it off you will waste a lot of battery power and deplete them quicker
Unless you are trying to run the microwave for short periods of time and have a large battery bank (4 6volts or better) I would suggest a small inverter sized just over what ever devices you are trying to power. Cost less money and wastes less energy
How do you plan to recharge batteries in the places you describe? You either need enough battery bank to accommodate the time you plan to be there with inverter use or solar to recharge if generator/shore is not available.