Service tax rate

Dear Friends, kindly calrify my doubt on the following case.

Mr.X doing a Consulting engineer services (Proprietorship Concern) and he received a draft work order from a Company say ABC Ltd for Rs.110300 (incl.ST @ 10.3%).In the work order, the Company has mentioned Date on which services started was 29.03.2012.

First question is since the work order issued by the Company, should Mr.X needs to issue the invoice separately for the amount what the company has mentioned?

Second question is whether the service tax @ 10.3% is correct or 12.36% to be levied?

Third question is, if Mr.X received payment after 01.04.2012, what is the Service tax rate applicable?

regards,

Mukund.