It's up to you. The main quest line seems to work better if you're being reasonably nice, but you can be an evil overlord in a fortress with walls made of people if you wish to. The difficulty would not change much.
Yes, male MC can personally satisfy all the native women around him. In fact, you can give a harem to every man who works for you.
Female MC is less enthusiastic about sex, but with the right conditions, she can sleep around with male natives too.
Named characters are more complicated, you'll probably need a guide to make every named character part of your harem.
John's guide has some recommendations: https://f95zone.to/threads/mad-island-v2024-05-23-e-made.209671/post-13838706
Use magic! Specifically, put a bunch of leaf figures somewhere to reduce the number of people in a raid, and use blue smoke signals to slow down the raids.
You can just pick up your buildings and people, and move them to a new location. It will take some time, but it should be easier than restarting.
