I use frostwire and all my virus and malware goodies are up to date. My computer blocks a lot of beacons, analytics, cookies and virtually all forms of advertising. If your up to date and use judgement you should be ok, YMMV.
I use FLAC (lossless but much bigger files) files because I can hear the difference on my home setup but for a car CD an MP3 is fine, besides you can fit a lot of them on a CD. I use EAC to rip FLAC files from a CD and it works to put MP3 files onto a CD. On most of these programs you can simply put the MP3 files on a CD, or you can burn an "audio CD" which is probably what you will have to do to have it work in your car line any commercial CD would.
Not all cars will be able to read home burned CDs but most newer ones will. Even better if you have a stereo with a USB port, then you can just throw buttloads of stuff on a thumb drive and listen that way.
I have a 20+ yr old Lexus with stock CD changer and it works for MP3 audio CDs. My wifes 03 Acura works with that too but our old POS Buick did not play them.
Good luck