Mold remediation order

We just moved in our home last week and tested and have elevated levels of mold in our home. There is nothing visible on main level but tests confirm there is elevated levels. The source is in the basement and is believed to have entered the HVAC system and spread throughout our 4000 sqft home. I have extremely high sensitivities and am experiencing health issues already. I have heard 3 different solutions and am confused. What is the best order to do remediation? Kill source, then hvac system then hepa vacuum house?? will this get rid of it all?? Thanks!