So I now have enough MP to put 20 points into boosts for Shingen. Following the guide, I've pumped 6 pts into the 2 Burst Damage Up, 1 point into Atk(+++), and 6 pts into Combo Rate ups. That leaves me 7 pts and I'm not sure what to best use it for?

If it helps, here's the team setups I currently use w/ Shingen. My grids are not fully built yet (on average, 3-4 SSR weaps w/ Skill levels ranged from 5-15 + SR w/ Element Assault skills)

Wind: Cybele U, Cu Chulain, Azazel, Gaia (AW) / Other SSRs: Titania [AW], Arianrod, Nephthys [Wind]
Thunder: Tyr, Jupiter, Raiko, Athena / Other SSRs: Baal U,
Light: Michael, Frey, Sol [AW], Eros / Other SSRs: Atum, Metatron
Dark: Satan [AW], Hades, Osiris, Amaterasu [Dark] / Other SSRs: Amon U, Pluto, Berith