The best way to migrate data to Zoho CRM and link them all together?

The best way to migrate data to Zoho CRM and link them all together?

Hello,

I am about to migrate date from a CSV file to Zoho CRM. The CSV file contains several data: 
  1. Contacts: This should go into the regular "Contacts" module
  2. Companies: This should go into the regular "Accounts" module
  3. Subscriptions: This should go into the custom module "Subscriptions"
  4. Invoices: This should go into the regular "Invoices" module
So I am trying to find the best way to import this data into all the modules and link them all together. I assume that I need to import/migrate the data in the above order (first all contacts, then companies, then subscriptions and then invoices).

And the next part would be to link all records: 
I.e. the Contacts module should be linked to a company (if the contact is a company address), then the contact should be also linked to the subscription and invoice. 

So I was wondering what would be the best/easiest way to import all of this data? Should I split the CSV file into 4 single CSV files: Contacts, Companies, Subscriptions and Invoices and link them all together with something like a unique identifier i.e. a unique ID (to be sure that all is linked correctly). Unfortunately I cannot use the email address as identifier because some contacts don't have an email address. 

Or can I import the contact and create a new record for each related record? I.e. I migrate the contacts and create a company, subscription and invoice during the import. 

Thanks for your suggestions, 
Michael