In a ideal world you would take folate prior to conception, but the reality is that this doesn't always happen. If you have a good diet and have started taking it i should think you have nothing to worry about. I started after conception with both pregnancies.

I don't take pregnancy multi vitamins as they make me horribly ill. I am constantly concerned about my vitamin intake though, i try and ensure i have a balanced diet so that neither myself or my babies miss out. It's not always easy when you feel like rubbish.
You don't HAVE to take a multi but it is an easy way to ensure you get all your required vitamins. Elevit is the most expensive, you can take a cheaper one if you want to take one.

As for feelings in the first week. I knew i was preg b/c i felt sick.

Best of luck with your pregnancy.