Maintain of service tax books seprately before registration or not

CENVAT Credit on Input service are available only if the service porvider is providing "Output Service." 

Since the assessee is not registered under service tax as the turnover does not exceed Rs. 10,00,000 limit, All the service provided by the assessee are considered as "Exempted Service" i.e., These are not an "Output Service".

Thus, Assessee shall not get Cenvat Credit on Input Service.

and what will be the accounting treatment of input services we will treat them as an expense or maintain seprate books of service tax.

Yes, It should be expensed out straight away.

and on what amount we will deduct tds expense+service tax or only on the expense amount

TDS to be deducted only on Expense amount excluding Service TAx amount.

Thank you very much