Hi Siri,
You can combine Test Cases and their Test Case Steps in a single excel sheet and import it all in one-step. Check this out, it has a sample of such a template: Exporting Test Cases and Their Steps
You may be able to use the DB Connector too, but I'm not sure it's going to be easier than using Excel. If the number of Test Cases and Steps is so very large, you may want to split it to separate spreadsheets also for your own and maintenance.
I hope it's helpful.
Sagi