I'm currently going through this process and there's some bureaucracy involved:

1. You need to show that you have financial resources of 100 000 SEK for one car and 50 000 SEK for all subsequent ones you're registering for. This needs to be reviewed and attested by an auditor. https://www.transportstyrelsen.se/globalassets/global/blanke...

2. You need to be a certified traffic manager. https://www.transportstyrelsen.se/sv/vagtrafik/Yrkestrafik/G...

Nothing super complicated but it's not just getting an extended driver's license like OP says.