Is it possible to add config, that prevent them from spawning inside base (or attacking base)?

To be played on peaceful mode, and fight them only when expanding.

No. In factorio it is very hard to know what is "inside base" in that open world. The mod was thought to perform a real invasion, from the ground to surface. Many things will be destroyed for sure. Robots should care of the repair...

Is there limitation on which size land they will spawn? E.g. will they spawn on the island that is smaller than 10x10?

Maybe. The mod searches a random place in a chunk (32x32 area) where something was built by a player

That would be a good idea^ I heard biters won't expand within a 100 blocks of player entities. Anyway to implement that same idea with configurable settings? You have an awesome mod on your hands man but I feel it's just for players who want their base destroyed. Keep up the good work

Edit: maybe set it so biterzilla can only spawn from a spawner or giants worms only spawn a certain distance from exsisting biter bases and obey the expansion distance of E.g 7 chunks?
Again great mod man, I've been looking for a long time for a mod that adds massive threats like this

Thanks for your suggestions. Maybe I will think a way to do this for the big ones

That's sweet, I'm looking forward to this!