Is it a given? Let's see:
-25% A Amon
-20% C Thanatos
-10% Resistance Satan Awakened
= -55% total
You're already past the 50% cap without Sniper Shot. So use PF instead.
The "which Soul should I use?" thread should answer that. I don't think your teams are fast enough for Shingen until second anniversary patch, so Hercules it is. Shingen's only real benefit for you right now is the ability to use an EX skill while still having PF, so if you need defensive tools, that's probably the way to go. Yeah, Herc's def debuff will be "wasted" but Herc is still just way too good to pass up on.See above.