1. I will have to think this a lot while making different types of effects, for the start, there is dawn, day, dusk & night, and for the realistic experience sunlight and the light effects change with the clock so basicly it will get darker with every hour after day is starting to switch to dusk and brighter when it starts to switch from night to dawn and from dawn to day. Hopefully you get my point, if not i will answer it better on next post.
2. That is the size i want it to be because it would feel more realistic and represent an actual country more than just it being one map that isn't even a country. But i know its hard to make it so big so it will start as smaller one and with updates it will get bigger with new towns, villages, etc.
3. I think part of survival game is the fact that more realistic it is, more people will actually enjoy it instead of game that is just like a badly animated game with bad graphics because realistic land and other stuff make it feel more alive and more like you are actually in the game yourself. This is just my opinion, everyone has their own and i respect it, i just like realistic games :p
Btw adding this to question number 1, there will be more effects when game goes on with more updates so there are different types of effects for dawn, dusk, etc