Bulk importing categories into WP

I am migrating my website from another CMS to WP.

I have a csv file with more than 10,000 rows with 6 columns – continent, continent_id, country, country_id, city, city_id.
I wish to import these as nested categories in WordPress with the category name as slugs. There will be 3 levels (continent -> country -> city)

I need a solution which would help me do this efficiently – it can either be a plugin or a php script that I run once to import the data.

If I am not wrong a custom taxonomy would solve it, but I’m not too advanced at WP and not sure how to build a solution myself.

The challenges are:
1) Some city and country names are the same (e.g., country-> Hong Kong, city-> Hong Kong). WordPress does not allow duplicate slugs. In this case it is OK to add a 2 behind the duplicate (i.e., city) slug to differentiate it from the country slug
2) I want the continent, country and city IDs to be preserved somehow as as I need to bulk import posts into WP later using the IDs as identifiers linking the posts to their respective categories.

Any advice or help would be much appreciated!