I get all this stuff about 300 being enough, or it being a starting goal, but GTA V already gets boring with the amount of players it has. I imagine 300 on a map twice that size will still have some emptiness to it which will kill the immersion. Unless there are going to be NPCs then this is a big negative. The city would feel too quiet.
My biggest confusion with all of this is, how will leaving a server change anything? Will I lose all my stuff? Will houses be instance based (That would ruin it a lot for me)? If 300 people are playing on a server, what happens if two people own the same house? The only possible idea I have is that you'd lose everything when you leave, but that sounds like a nightmare.