Is erasure of MacMini drive and reinstallation of High Sierra my best option?

Last week was hit with RansomWare but managed to escape. However, the next day when I ran High Sierra 10.13.4 and Safari 11.1 and tried to view Google News, I got a redirect screen repeatedly. But I had no similar difficulty when I used Firefox to view Google News. Yet all sorts of strange things keep happening from time to time.

For example, data files in several windows now have zero contents. Some time after that discovery I opened a window that contained a number of various files including an old Quicken Essentials data file. I watched as the top file became highlighted and the highlighting moved down file by file until it came to the Quicken file and stopped. I thought to myself, "That's odd--never seen that before." But later when I opened the window again the Quicken file size had changed to zero like had happened to some other files.

Although I already had two recent backups of my Mini boot drive, I made another. I suppose it will be infected with whatever malware is causing these strange things. So I'm wondering if the only solution is to start over with a clean re-installation of High Sierra. If so, how do I go about that?