success..95% or so :)
wanted to follow up here.. some of the terms finally clicked in my mind to understand the functions of recovery/fastboot/bootloader/flashing..etc. I wonder if there is a flow-chart type diagram available out there--that type of thing would have really helped to understand--being able to visualize where these different aspects interact and where files etc line up with them.
Short version: successfully running GPE rom smoothly and enjoyably on a 'clean' system.
needless to say I used TWRP to backup my system. And Titanium for specific apps. Used rsdlite to flash the GPE rom from the forum here. Then I factor reset the rom, then I think I formatted internal storage space?? --at that juncture I was a little less clear what the specific sequence should have been to 'start fresh'. Should I have factory reset my device before flashing the rom? Or maybe it really doesn't matter.
Thanks for everyone's help. One thing that didn't migrate over through gcloud backups--embedded images in text msging program. relatively small loss though