Dear,
As you written that your Total annual Turnover is only 4-5 Lacs annual.
GST is applicable only when your annual turnover is reach to 20 lacs.
service tax in not in exist now.
although you want to take registration than you can but it is not compulsory to your business.
if you get registration than you have to file the GST Return every month and charge the GST on your bill.