RCM RCM

You can consider first 2 invoices under 5000 exemption and invoice under RCM can be prepared for Rs.2000.

Also note that you can issue one invoice in a month for all such purchases rate wise.

Make a note of all such purchases, prepare a consildated invoice at the month end for each tax rate.

In case of GST, the levy of GST depends on the time of supply. If the receipt of payment is earlier, the supply is deemed to have been made. Thus GST is chargeable on advance. Full form of RCM is Reverse Charge Mechanism

In case of procurement from unregistered dealer, you need to generate self invoice and pay GST accordingly.