Question3: One of my client has cross his threshold limit in the month of November 2017 but he has not got registered in GST while his business is continue till now. Now he want to take registration in GST. What would be the obligations & penalty on late registration'

Answer: According to Section 18(1)(a) If the registration in GST are taken after 30 days from the date on which liable to get registration then you are not eligible for credit in respect of input and input contained in semi-finished or finished goods held in stock.on the day immediately preceding the date from which you becomes liable to pay tax under the provisions of this Act.
Effective date of registration in this situation shall be the date of grant of registration certificate. Thus You can collect GST and issue GST invoice only after getting your registration certificate and can claim ITC on purchases made only after getting registration certificate.
If the person is caught for this default their will be a penalty under section 122 i.e
Rs 10000 or
An amount equivalent to the tax evaded,
whichever is higher. (Reply dt. 12/3/2018)