1. Yes, there are few methods of downgrading, using downgrade PUPs through recovery or QA flagging. There are some advantages - no need for for the games with FW 3.41 - 3.55 to patch anything manually, it works straight out of the box. But new games (3.60+) are not playable, wheteher you have a backup or legally owned game, it can't be played on CFW. And NO PSN access on CFW is possible yet by any means.
2. What do you mean, work. PSN doesn't work. Period. If you Purchase new game, you should upgrade system and say bye to CFW
3. Kmeaw is most stable one, do not have hardcoded LV2 patches (unlike Waninkoko CFW) and not bloated like JFW. Also, it can install pretty every package file.
4. Hmmm, no that I'm aware of. There maybe still.
5. Depends on what is patched, by my guess is, what you read was for eboots.
6. There was only one version, AFAIK, grab it here: http://rghost.ru/4048423
. Be sure to read a lot of instruction before doing this, also be sure to install OFW 3.55 first
7. It's the best, IMO