MrX4353: ...
1) Would CDPR issue me a Steam key if I already own the GOG.com version if I asked?
2) GOG Downloader problems, any foresee-able fixes for "Checksum error" and/or empty folder downloading?
I don't think they will hand out a Steam key, but who knows? Give it a try, it doesn't hurt.
As for the GOG Downloader, start it and click on Settings. Set "Number of concurrent connections" to 1.
Make sure that there's enough free space at the save location and that it isn't formatted in FAT32 (because of file size limitation).