FORM FITTING V neck black cardigans are the way to go, maybe you could get away with navy blue too. But I definitely know, you can't go wrong with that^
As far as other colors and neck styles Ms. Anonymous below would be right. Don't go with light colors! And if you do try my suggestion, you would be able to tell if you look like a regular stylish guy...or a grandfather.
Depends on where you wear them to, how you wear them, etc. If a guy can pull it off and knows how to wear one then I think they can be attractive. You want one that is form fitting too. A big baggy one can make you look older (not in a good way) and very messy. As for the colors, it depends on what looks good on you. Yes, light colors can be worn and still look good. But only if the color fits/matches you well. As for the lacoste shirts, I can't really tell you since I'm not familiar with those particular type. Post a link?
I think it depends on the guy really. Some guys have different looks to pull different articles of clothes off. I think they're both good looks. Try both on and see if they fit you the best. See if you like the way you look in them and if you do, then I'm sure women would like them as well.
Some guys do look good in cardigans, while others look like their grandfathers. When you look in the mirror you should be able to tell. Stay away from overly light colors and sweaters that are too loose.