Gaining possession and recovering rent

Possession - Section 8 and Section 21

I spoke to Dave A on the phone yesterday but just want some clarification on a few matters.

I am acting on behalf of the owner of a property. The tenant owes a substantial amount of rent (well over 8 weeks) and now her benefit has stopped so I need to go ahead with an eviction.

The tenant has been in occupation since the original tenancy dated 11/04/11. This was renewed on 11/05/12 both were 6 month terms. The deposit was protected and I also gave the tenant the prescribed information when she first moved in. I also served a section 21 notice with every AST.

You advised that the best option is to rely on the section 21 that has been already served and now use an N5B form to make a claim for possession. The questions I have are:

1. If the possession is gained this way and not with a section 8 is it possible to make a claim to recover the rent and if so how is this done? Can it be done through https://www.moneyclaim.gov.uk/web/mcol/welcome ?

2. If the tenant is a housing benefit tenant and has no money to pay could the money she owes be deducted from future benefits (I know that while she has been at this property an amount of her entitlement was deducted to pay a previous debt)

3. You mentioned that you provide a service to check that all the forms are in order. How to I go about using this service as I want to be sure that the section 21 that was served was correct and the N5B form will be correct?

4. I use a PO BOX address on my AST and Section 21 form as I have previously had threats from tenants and do not want them to know where I live. Is this a problem? someone previously told me it invalidates the section 21.

5. The owner is on holiday until after Christmas. Does he need to sign the N5B or can I sign it on his behalf?

Thank you again for your help.
Kind regards,
David.