I have no idea about CCP, but the pronto hex codes for the Harmony PS3 adapter have been posted on this site, and there are JP1 codes on the JP1 site. There are probably ways to get those into a URC.

I've had very mixed results with most MCE dongles. I have an Flirc dongle, but I've never actually used it. My Ortek and Diamond dongles work perfectly for standby every time and do everything I need.

For complete power off, you'll need to build or buy extra hardware for that. More trouble and expense than it's worth IMO. The half Watt you'd save wouldn't pay for the $30 hardware for about 100 years.

I wouldn't bother with Plex unless you have a lot of phone/tablet clients. Otherwise the picture quality kind of stinks due to all the transcoding Plex does.