I have no idea why you were modded down. You're absolutely right.
The OP apparently learned just enough to form those ideas and questions, but decided not to continue reading and find out that (more or less) all his proposals are already done.
1. On/off switch for "internet access". There's bunches of ways to do this. Many laptops come with a hardware switch to turn off wifi... that can do the trick. Just about any firewall software could do it, and most have a "panic" mode (including the very naive
2. Start browser in fresh (virtual) space, but pre-populated with saved cookies. I'm ignoring the virtual/sandbox stuff, as it's unnecessary (but could be done via docker, a vm, bsd jails, chroot, etc). The browser can clear any and all data at the end of a session already, and can optionally not clear the cookies. There's also a cookies setting for "keep local data only until you quit your browser" allowing cookies to be created, but then those created during the session go away when you exit the browser. There are exceptions, third party blocking, and cookie managers.
2 - b. A good database of all the files in "my virtual space"... use your file manager. If you want to know what was newly created, use existing filesystem tools. You can even check the ~/.mozilla or ~/.config/google-chrome into git and diff it afterwards, or use etckeeper to maintain it, or a IDS like tripwire. Whatever level of detail you want.
4. When you decide to exit the browsing session, at least, the computer should save important cookies from sites you frequent for later restoration.
Already done. See #2. If you want a partial save (only those you consider important, but not other ones you don't want), then you'll need to become more intimately involved with your cookie management. Start with the cookie manager and figure out what you want. Then script something to maintain your cookie DB as you see fit -that isn't really as hard as it may sound. The cookie DB is often a flat text file, or an SQLite DB. Google Chrome's is SQLite (on linux, ~/.config/google-chrome/Default/Cookies)... you can use "sqlite3" and sql to manage it directly, or script something using your favorite language.
5. Shred the virtual space on exit.... if you really want this, then a short shell script can do it. Create loopback encrypted filesystem; mount; copy skel of browser directory into it; start browser using that profile; when it exits, copy out the cookies, then unmount and delete the file. I doubt that's really what is wanted though - have you thought about all the side effects?
3. Why is it so hard to find the specifics of, step-by-step, how (not why or if) we are being conned and raped...
WHOA! Hold up. This is not rape. You can watch every bit of data go back and forth, and you can control every bit of what you send or accept. Worst case (you don't trust the browser), use a local socks proxy and do your filtering there.