@ADITYA RAJPUROHIT With respect to the size of your data set I think you can use the least available VM type for your subscription. I would recommend CPU type Standard_DS11_v2 for light weight testing or Standard_E4ds_v4 if you want more cores and RAM.
Also, since you are planning to use OpenAI deploying an endpoint of a base model should automatically take care of compute behind the endpoint as it is managed by Azure. Creation of VMs in Azure ML might only be required for data manipulation tasks or processing. If you create a compute instance ensure you shutdown your instance when not in use or schedule automatic shutdown when idle to reduce costs. I hope this helps!!
If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.