Originally Posted by Deusdies
I have a very similar problem, though I don't consider myself new to flashing.
I did advanced wipe (system, dalvik, cache, and data), though TWRP was complaining about being unable to mount /cache. I also had to select "use rm -rf instead of formatting", because formatting didn't work (recovery would reboot). Then I tried flashing the ROM linked (the GigaWatts Pro), but it would not boot (gets stuck on black screen after boot logo).
Since I had a backup of the stock ROM, I figured this wouldn't be a problem. But now TWRP can't mount /system and therefore I can't restore my backup - it just says "failed".
Try a factory reset? I'm not sure what it does after you've already wiped everything. I've soft bricked my tablet in a similar fashion with the same symptoms as you except TWRP wouldn't even load after a couple mounting failures. Here's what worked for me. I downloaded the stock firmware for my tablet from here: http://www.sammobile.com/firmwares/
Enter your model # where it says "search device here..." and download for your region. If you're in the US you'll want Cellular south. Extract the .tar.md5 file then run Odin 3.09 as admin and install using the AP button. If using Odin 3.07 use the PDA button. I'm pretty sure I had to re root and reinstall TWRP after that. I was then able to restore my backup. I've soft bricked my tablet a few times playing with custom roms. Hope this helps.
I'm fairly new to this, so if I've made any mistakes, someone please chime in b4 Deusdies reads this.