I have no idea what Tor is. Both 9/11 and the Patriot Act occurred in / are from 2001, over 20 years ago. The major computer operating system back then was Windows XP. I'm not an IT person but I have to wonder, "if" one could source that vintage of hardware and install Windows XP, how well it might function on the current "inter web". Finding XP should be fairly easy, I probable still have Windows 3.1 on diskettes laying around, though finding them may be another thing
If you are going to be this paranoid you might want to keep your commerce off the 'net altogether and advertise in the local "Giant Nickel" or whatever your local classified advertising periodical is called, or the classified ads section of the local newspaper. An issue with that though is fewer today look at print publications, but many still do. Also, many locations still have kiosks and bulletin boards where one can post flyers.
Another thought is to go to the public library and create the marketplace account from their computer, and only access that account from the library computer, so there is no connection back to any info / cookies on your personal computer. Any pictures you may need to post can be brought on a thumb drive.