I use +Atk -Nin Because other stats are kinda valuable in pvp

I have +Atk -Def. I have my own reason why.

Life recovery does not affect leech, but it adds HP recovery at the end of the round. It is OK, but I personally do not prioritize that stat. Get the primary stat like HP, Atk, Nin, Res, Def first. then you focus on secondary stat like damage reduction, HP Recovery, Atk/Nin *ion. etc...

Yes mood stays between switches, strengthening equipment should be prioritized over group skills. (this due to the convoys giving you enough for grinding gs as needed.)

And of the 8 inner gates, it's best to worry about Nin,Res,def, and crit early on, then combo,injury, regen, and hp later on as needed.

Re-mooding each main switch isn't really too important unless you pvp.

---ofc this is just my opinion--- be you, see what works.

First of all you prioritize what you will play mostly, then you add the mood wich think suits better for you.
If you are going to play Lighting/Earth(as a dps) then you will need +ATK mood but dont go for -DEF or -RES because you need them.Like Raikirin mentioned you can get -NIN wich is useless for this characters.
You c*so go to your Character then Details and check what skills use mostly (if it is TAI or NIN) and then decide.