Service tax to lawyers/advocates

A lawyer/advocate is providing services to all categories of service receiver i.e. business as well as non-business entities having turnover less as well as more than 10 Lakh.  Legal services as per Service Tax Rules is covered under reverse charge mechanism.  Now my queries/doubts are:

Situation 1 : As long as lawyers/advocates gross receipts/turnover is below 10 Lakh, one is not required to register under service tax.

Situation 2 : When one is crossing or likely to be crossing the basic limit of 10 Lakh

1. Whether the service providing lawyer/advocate is required to obtain service tax registration in view of the fact that the category of service is covered under RCM and business entity is suppose to pay service tax?
   1. If yes, then once obtaining such registration whether he/she is availed of basic exemption of 10 Lakh or he/she has to charge service tax on all previous bills as well?
   2. Whether service tax is to be charged to all categories of clients (business and non-business entities) irrespective of their turnover criteria set in section or only to non-business entities?

Thanks