Ditto the Mini route, check out eBay too. 8GB RAM should do the trick unless doing heavy music or video editing. And, the internal 5400RPM drive is a bit of a bottleneck, options are to use a Thunderbolt2, USB3 external drive as your boot drive with an SSD in it, or to put a SATA3 2.5 inch SSD drive in the mini in place of the 5400RPM drive. The latter is a bit of a chore, but follow iFixit's guides and you should be OK if you are at all handy with computers.
Apple provides a migration utility to pull settings and files from old PC or Mac, in my experience this works pretty well. On first boot on a fresh install, it will ask if you want to import files and settings from a PC or Mac. Or, navigate to
Applications > Utilities > Migration Assistant.app to launch the tool. The tool will import My Documents including Music, Videos, Pictures, and Documents, as well as bookmarks from browsers. Also, Apple has a online guide for PC switchers
https://support.apple.com/en-us/HT204216 and
https://support.apple.com/explore/new-to-mac are good places to start. Also, Apple Stores offer free 1 hour workshops and will tailor the lessons to participants, especially if you are in a small class. These workshops range from novice, to more advanced as you move along the learning curve.
As for the external drive with iTunes content, if it is FAT formatted (vs NTFS), should be able to plug that into the mini and it should be transparent following migration of everything from the PC. If it is NTFS, back it up to another drive, reformat it as FAT, then copy everything back to the USB drive. Make sure the name of the drive remains the same so when the Mac mounts it, the relative path to iTunes content will be the same as the entries in the iTunes library.
Good luck, and welcome to the Mac family. You won't regret it, but be patient, it does take a little time to get familiar with differences. Most PC apps have some sort of equivalent in the Mac world, Google is a good friend when it comes to finding these. And, use the forums, including Apple's support forums as well as Mac Rumors and others. You will find that in general, Mac users are quite welcoming of newbies and willing to help. But, be sure to mention your newbie status so folks understand where you are coming from and will be more patient with your seemingly dumb questions.
And, don't forget to attach a USB drive (or partition the existing USB drive if you have 500GB - 1TB free) to use as a Time Machine backup. Time Machine is a very good backup utility and once setup, will incrementally backup everything on your Mac every hour. If you get in trouble, your backups can be restored on a fresh install and all of your files, settings, apps, everything will be restored in short order, far simpler than PC restores in my experience.