How many flash drives would this take and at what cost, and how many hours (or months) or ripping CD after CD into my laptop
The size of the music files will vary, depending on how they are ripped and (of course) the length of the track. Looking at some music tracks I've ripped using iTunes, I see file sizes between 5-10 MB per file. These are mostly in the length range of most songs today, about 4-5 minutes. These are in the MP3 or M4A format. So you could probably store between 2500-3000 music files on a 32GB USB drive. But you can get much larger USB sticks for well under $50. I can find a 128GB stick online for only $10, but I'd probably spend a bit more for a name brand. So storing more than 10,000 files should be easily done on a single USB stick.
I can't argue with the fact it would take some time to rip that many files. It's not difficult, and there's many free software programs that can automate the entire process. But that still requires you to put the CD in the drive and remove/replace it with the next one. Yeah, it's going to be a tedious process. But it's worth the effort in the end. You mentioned your computer doesn't have an optical drive, so you'd need a portable drive. That's what I use on my wife's computer, which doesn't have one either. As for where to store the ripped files, you can either rip them directly onto the USB stick (although that will likely be a hair slower) or use a portable USB drive for that purpose as well. Then you don't need to open up your computer and try to install another hard drive.
I've ripped all of my DVD/Blu Ray discs to a media server. The cost is a bit more, simply because the files are much larger so I need to add significant hard drive space in my media server. I have a couple of 8TB disc drives, and a couple of 4TB drives, and I have them maybe half full. That amounts to over 6500 movie and TV episode files. The 4K rips are the largest, with each one in the 50GB range. DVDs run from 3-6GB per file, while the 1080 Blu Ray rips are in the 30GB range. A 30 minute TV episode might only need 1GB of space.
I can't say why they have dropped CD players from cars, although I can guess that it's a) cost savings and b) more and more people are putting their music collections on their phones, which then connect to the car via Bluetooth and stream the music. It's much easier to play your personal music over Bluetooth (or using CarPlay/Android Auto) than swapping out CDs while driving. Also, don't forget that leaving a CD inside a parked car on a hot day is very likely to severely damage the CD, making it useless.