You're scaring yourself away from these experiences. If you managed to pick the parts out for a computer then you can assemble it. Picking them out and making sure they're compatible is the hard part. Assembly is just putting them into slots that only they can fit into and plugging in some wires.

Installing an OS is also (usually) trivial. You download the software online and put it on a USB drive and follow the instructions. Dual booting takes a little more effort because you have to set up partitions, but it usually isn't that bad. I'm 100% Linux though because when I dual booted starting from Windows it eventually destroyed things after a Windows update (because Windows sucks), so I just removed the Windows partition and redid everything with just Linux.