Win10 made me finally ditch Linux. But one thing I miss was the ease of customization. Are there any free tools to do this on Windows? I know there's Start10 and all that, but I'd prefer not to shell...

Get more RAM, disable Superfetch and automatic defrag, disable Windows Defender and use Common Sense 2016 instead, yeah. There are a lot of things you could do. I used to run Win8.1 on an old laptop...