With respect to insurance, I strongly recommend that you shop around for the best quote.
A specialist childminding insurance company quoted me, on average, £300 more than ANY of the other companies on a like-for-like basis. Moreover, they tried to pressurise me to take up the insurance there and then, and got quite stroppy when I declined. Worst still, when I asked them to send the quote in writing, they refused. I did receive an e-mail afterwards saying that the quote was enclosed as an attachement, but when I opened the attachment, it was a blank page/screen.
Bear in mind that you need both a household insurance and a public liability insurance. If you intend to use a car, you need to make sure that the policy says the car is used for childminding purposes. Make sure everthing is in writing.
When shopping for my car insurance, one insurance company mumbled something about passengers not being covered. She would not clarify what she had said, so I gave that one a miss. Make sure the company is clear about the level of insurance cover you require - do not rely on them to figure it out for you.
As Flisspaps says, you really need to go to a pre-reg briefing session to get an idea of other expenses.