Having built your own computer says to me you've got the smarts, interest and patience to learn about your computer. The hardest part for building my computer was finding all the parts that would fit together, this CPU is compatible with this motherboard and this RAM, etc. Plus, building a computer yourself means you've done #1, you've installed an OS on it. You're no stranger to the BIOS, partitioning a drive, etc.
I can really get wanting an OS that doesn't take all your time tweaking. This is why I use Linux Mint; it comes pretty complete and usable out of the box. The "customizing" I've done to my Mint system included changing the wallpaper, installing a new theme from gnomelook.org, dragging a few things around, and such. What I've found over the time I've used Mint, it doesn't change so drastically with each release the way Windows does, so I don't have to spend time re-learning where they've hidden the Save button this time. I can learn new things.
I do strongly recommend keeping a Windows machine around while you learn and transition to Linux. I started using Linux on a Raspberry Pi back in 2014 or so because I was tinkering with electronics and ham radio, and wanted a little computer to attach to my radio to run FLDIGI that wasn't my big expensive laptop. Then that laptop died, and I bought a new one that came with Windows 8.1, and I hated it, so I tried desktop Linux. That laptop still has Windows 8.1 on it to this day. That machine only had one hard drive bay so I was able to dual boot by partitioning the drive. If you have room in your case for a separate drive, I would recommend doing that, and keeping Linux on a separate drive to Windows. If you have an old computer you're not using lying around, like your old machine or something, it can be worth using that to tinker with. Try out several versions of Linux on hardware you "don't care" about. It can be freeing to not have to worry about borking your Windows install. Using a separate drive is a great idea and you definitely know what you're talking about.