steps 4 + 5 can be done with the libreELEC USB SD creator downloads – LibreELEC this is what i used a long time ago. Once its installed its easy to update.
Cant say i remember anything about J4, how i remember it is power the slice and connect the USB to get to the eMMC, dont power the Slice and connect the USB to get to the internal hard drive.
8.90.008 was released today so you can also grab the files from update
8.90.008 looks good to me, quick test on movies, tv shows, music, game roms all working through HDMI. 
its definitely slice with power, this will get you access to flash the image. Without power gets you access to the hdd where you store your videos.
just keep trying different combinations of powering on and connecting, it can be temperamental. Also change usb ports (maybe an old usb 2 port?)
Also if you haven't already, remove the supplied RF remote dongle, I'm sure that's caused me to have performance issues to.
Good luck!
I would second the CM3 upgrade, a much better user experience all round, though you'll have to sort out a heatsink.
Have you tried switching between the ethernet and the supplied wifi dongle to see if theres a difference? also does this happen on SD content?
Havent streamed any blurays but have streamed HD broadcasts via wifi with no issues on CM3.
Are you running CM1 or CM3 in your Slice?
CM3, its overclocked in the sense that its running at a constant 1.2GHz
I don't seem to have any problems with 8.2.4 but i have already turned off the RSS feed is yours switched on?
