I think a bigger deal is being made out of getting flash on 4.1.x than it should be. It's as simple as
this.
Flash doesn't support 4.1.x, but pretty much everyone who has upgraded has reported it to be working fine. I have it running on a Evervolv 4.1 build without any problems.
WRT to battery comsumption. Titanium backup to freeze unwanted stuff and a power-friendly CPU governor should increase that substantially. NQ has an add-on to their anti-virus that kills all non-essential tasks that are running, not sure if it's separate in the Play store. You can probably find it separate as an apk on someplace like xda, anyway.
Friend Stream doesn't seem to have a port from what I saw while looking at XDA. You could either put a Sense ROM on the S3 and then enable Friend Stream with third party apps or by editing an .xml file, or you could try
this. Link is the closest thing I could find on xda. That wouldn't be so different from your Friendcaster idea, though.
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