Composition scheme under gst

Yes you need to be registered under GST, As for claiming ITC, a person needs to be registered and as per section 22 Person liable for registration are Supplier of taxable property over 20 lakhs and people already registered under existing laws. Read also the following:

'What are the conditions necessary for obtaining ITC?

Ans. Following four conditions are to be satisfied by the registered taxable person for obtaining ITC:

• (a) he is in possession of tax invoice or debit note or such other tax paying documents as may be prescribed;
• (b) he has received the goods or services or both;
• (c) the supplier has actually paid the tax charged in respect of the supply to the government; and
• (d) he has furnished the return under section 39.'

Note that for issuing a tax invoice/return you need to quote your registeration no under GST