Input credit of service tax - Set off of service tax liability - Service Tax

a company whoes turnover is exceeding Rs. 1 crores but product manufacturing is non excisable hence no excise is charged to the customers. However during installation of machinery the company is charging eraction charges on which service tax is charged. Now my questions are 1. whether all expenses paid on which service tax paid where input credit of service tax available can be reduced from service tax liability? 2. In case any item used for manufactuing of machinery as above includes cenvat credit can be used to take set off of service tax liability? 3. As there is only one service provided by company to its customer as specified above, whether 100% input credit can be availed?