Simultaneous turns is almost required. It's why people can log on and play their turns whenever they are able. Otherwise they have to play in order, which means turns will last much longer.
Take Over AI means that human players can take AI civs from them. It's not needed, but if it's probably easiest to leave it on to give yourself more flexibility as the administrator. For example, if a player goes AWOL you can Kick him out of the game, which gives it to an AI. Then you can find a new player who can take control of that civ. If there was no Take Over AI then you really couldn't do that. I'd definatly recommend having it on.
Also, I would recommend against allowing a player to take over an AI civ that
starts as an AI. Because the AI gets extra units, techs, and faster production it would be unbalancing to let someone take that over on turn 10 or so.
The rest of the settings are kind of up to you, and only really impact the game in ways you'd expect. though you can put them to a vote of your players if you like.
As for my own personal tastes, I think having maps that are a little bit more crowded than normal makes for getting to the interesting gameplay sooner. So having 10 on Standard instead of 7, or i you're playing with five then a small map... .things like that. This could just be me. I like to play on higher difficulty levels on games with no AI, because it only effects the amount of free happy and healty faces, thus making trading resources more important. I feel that makes for more interesting multiplayer.
The nice part is, as the admin, you can do whatever you want! (except make it non-simultaneous turns!

)