Hello. Is there any csv template for Sales order/Invoice/Bills/Customers/Vendors so that we can use it in Importing CSV records please?

there are no one size fits all templates for all these import types, it depends on your setup, locale and customizations. Your best bet will be to dig through suiteanswers for guideline templates. Another option is to create saved searches with your required field and use the header row as your template from the csv extract. https://suiteanswers.custhelp.com/app/answers/detail/a_id/48672/loc/en_US

You are right but NetSuite has fixed mandatory native fields

DM me I can give you some base entity type import templates

Thank you sir