I need to reinstall (OS? and gapps) after a part-wipe of internal memory of Manta, 5.1 After a failed change to CM13 ROM, my Nexus 10 booted to show only its screen still alive but with lots of green Androids (its name is..?) and unconnected icons. 

Inside are only 5 apps, no keyboard, no file manager, but there is 'Settings', 'Terminal IDE' and TWRP (2.3.3.0).  I do have a usable USB keyboard, I'm pleased to say.

I can run TWRP in Recovery and can see into the device with Android File Transfer running on my iMac. TWRP shows 'cm-13.0......zip' and '...open_gapps...aroma...zip'. AFT shows 'twrp...img'.  I can put a replacement stock Manta 5.1 .tgz on it via AFT, 'tho I can't remember if I need to 'un-tgz" it first.

In order to avoid a bricking, what is the safest option?  


Can I just install and run Aroma to replace the lost bits of the
Gapps?   
Should/Can I transfer the Android stock to the nexus and    install
that?    
Be brave and install the Cyanogenmod 13 and Gapps?


Your help will be appreciated!
In order to avoid a bricking, what is the safest option?

You're not going to brick the device by installing stock or cyanogenmod.

Should/Can I transfer the Android stock to the nexus and install that?

This is the safest option but will wipe all your data. You don't need to "un tgz" it. This will take you back to 5.1.1 that was updated earlier this year
See https://developers.google.com/android/nexus/images for instructions

Be brave and install the Cyanogenmod 13 and Gapps?

If you are going for a 6 custom version of android also look at the early AOSP builds or OmniROM. I'd recommend a factory reset in recovery, flash SuperSu  (if you want root) &amp; GApps then flash the ROM. OmniROM have started doing v7 builds

CyanogenMod deals with SU for you.