Bernice is one of the best tanks in the game, and is something to consider for your team.

Fignelia is going to be your best single target ranged magical DPS and is great for maps with super heavy hitting enemies that you want to stall their movement with.

I personally LOVE mikoto and drop her 1st, 2nd, or 3rd in almost every map. A def keep. The nice thing about mikoto is she frees up slots, as she preforms almost like a warlock and a witch combined. She will not have the wave clear that a warlock does, or the slow that a witch does, but does enough of both to be very useful for her skill and up. She can halt strong bosses or stop rush maps long enough for you to switch out something or generate that last bit of UP to win. Mikoto combos well with assassinate hi-jinks as well, giving you more hits for more proc chances (let's face it, some maps need that lucky assassinate unless you have a lot of cheap blacks that can instant skill to clear things).

I would pick Sherry as your melee magic dps. She is more attack oriented and will have a better AW for your current team. Sherry is the highest damaging princess as well I believe, getting higher numbers than the blacks with skill active.

Pick one melee healer over the other. Don't need two. Marr is a great healer to build as she makes poison and desert maps more bearable (yes, she reduces damage on placement in deserts, but you have to place her early to get any use from that), while at the same time having the output of a silver healer on multiple people. The male healer isn't a bad idea to build up, simply because you need male units for some maps. However, the gold female healers will out-class him. Camilla is considered by most to be the best pure-healer currently available, so that is something to consider as well.

One thing I notice is you have 4 physical dps ranged slots and no spica. Spica should be your #1 priority right now imo. I have never used the ranger, but I would imagine her and your gold archer are much less useful than other options you have. Plat archer + Marr + Prince + Gold Cannon unit can clear crystal G on their own btw, without need of additional units, (pending on how leveled they are) so getting the crystals for spica shouldn't be too much trouble.

Ditch the plat valk you have. She really isn't any better than Kerry (considering Kerry is much easier to cost reduce and place early). You already have princesses and aria as UP ramp, so I would put effort into other units besides her.

You have some great units