Dv 2008 Clarification

Can i use a sponsor's satement of account for as an evidence of support or must it be my own statement of account? How much do i need to have in an account of such?

For the Police certificate-Can i obtain it an keep till next year June/July when i am expecting my interview or should i wait till then? Does the police certificate expires?

How much do i need to obtain this Police certificate?

Please some who has gone through these processes should help me out.