Ansewers of your quaries:
(i) Unless your turnover crosses the limit of 9lakhs, you are not liable to get registerd.
(ii) in fact if anyone wants to take registration, without his taxable turnover limit, he can take registration and called as voluntary registration, but in such case, he is liable to collect service tax from 1 rupee service. On the other hand, if any person goes for regn after crossing the 9 lakhs limit, he would have another limit of 1 lakhs which is tax free. In other words, service tax would be charged on the billing above Rs 10 lakhs.
(iii) Yes, you can get the online regn nos. just go to site: aces.gov.in
(iv) You can not collect service tax unless you are got registered. If anything collected in the name of service tax without any no, this is advised to get at once the registration no and deposit the sum collected in the registered numbers. The registration no should be printed on your bill or invoice. No any other numbers are to be given necessary to collect the service tax.

