well ill just focus on your best opening move:
the way the rest of your turns unfold lie in what you see as effective thereafter, and following the theory that you should summon units from low levels up, like a lvl 2 (kurina), then maybe archer scout, then a lvl 3, then a lvl 4 etc. So that way you're not spending it on a lvl 4 as soon as you have enough for one and then being caught between reviving and spending on other units and grimoires. You'll be strapped for sp!
Increase your gowen lvl to 3 and summon brave soldier (you could just increase gowen lvl to two, but adding one more will render a 1st-turn shades' open skill useless as your sp will be at 0, but this is up to you though).
Now for the panther soul follow-up:
If their 1st-turn unit is something your brave soldier can take down right away, then think twice before pulling out that panther soul right after. Also, if they don't summon 1st-turn, because they're bringing out a tank, (which is typically the case) then pulling off the panther soul after you set brave soldier can clear that tank when it comes out. If you're not playing it right away then save it for when you're down to your second or last brave soldier, simply because they will start fresh with full hp after the revive and last longer with the added benefit of now being 50 HP, 60 AT, and 4 AGI (which by now you should know are brave soldier's stats after panther soul). Also, having at least 2sp at your disposal allows you to use brave soldiers slash action skill, which is incredibly useful in the mid-game when they're are probably 3 units side-by-side-by-side just waiting to get cleared from the 60 DMG that each will take (assuming they all have 0 DF of course, nevertheless, even with 10 DF, units with 50 hp will still get cleared).
A downside that stands out the most is having your brave soldier returned right after you just gave it semi-god mode with panther soul...which really sucks, and is part of the reason why I tell you to think twice before you cast it.
Although just mindlessly starting your duels with brave soldier+panther soul will probably occur on your part, it tends to work a great deal of the time. Just keep in mind that in the mid-game you can save it for a row-clearing force that could give you the edge you need.
Hope this helps.
EDIT: having ruby carbuncle as your first soul card will NOT get panther soul back as Gota just clarified for me, I forgot that grimoires don't go to your cemetery.