does migration wipe the previous PC clean?

Ah, then I'd recommend moving the data you want to migrate to an External Hard Disk and then do a drag and drop. You can attempt Wi-Fi however it is quite unreliable, my recommendation for a PC to Mac migration is to use Migration Assistant and ensure both computers are on the same network connected by an Ethernet connection. Please follow Apple's suggestions in Move your data from a Windows PC to a Mac - Apple Support. If you run into a hitch along the way then please call AppleCare ASAP and they should be able to guide you along. In the USA that phone number is (800) 285-2273, outside the USA please use the AppleCare Contact Info to find the number in your area. By the way, welcome to the light side!

No, a migration leaves the previous Mac completely as it was. If you intend to migrate from an old Mac to a new one PLEASE use the following as your guide if you want the most reliable, quickest and easiest migration. Setup Assistant and Migration Assistant. If you vary from these steps your migration may fail.

Following the steps in the "Related Article," will not delete data from the "previous PC."

Your welcome.