Sanaki build/team?

Seal Atk is decent, but IMO there are better B skills like Chills or Breakers. Also, I don't think you should give Sanaki Steady Stance when her defense is already too low to be salvaged. If you're still waiting for a Zelgius, BK is a budget option as well.
But then again, Bond skills are good choices for an A skill.

Ivs and build?

Ivs and build?

Several points that I think everybody will agree with:
- If she's your only 5* red mage, you're making a good decision putting her to work.
- If you pull a 5* unit, check their IVs. From their lv1 stats it is possible to know their lv40 stats.
- Steady stance is not what you do with Sanaki except in some extremely funky builds. You will get a lot more effectiveness out of her just blasting stuff to bits in a single hit (or depending on the build, possibly two)
- Seal atk is a poor try on her, and she can use other B-skills which are likely to do a lot more for her and for the team. You can use swordbreaker, axebreaker (probably overkill since most axes have low res and Sanaki already gets +20% atk for weapon triangle advantage), R tomebreaker, G tomebreaker, quick riposte (due to her good res), chill res, some other chill to support the team, wings of mercy on arena defense (or possibly even when you're playing her yourself), desperation if you're using one of her spd builds, and probably other options I'm not thinking of.

Now, the rest, most people will agree that there are multiple ways to do. If you're ok with locking her into this team, you have the team composition to use tactic buffs regardless of who fills the fourth slot. You have Sanaki (infantry), Maribelle (cavalry), and SS Camilla (flier), so any movement type is acceptable for the fourth teammate. I would suggest a solid DC tank with a lot of def because nobody else in the team has enough to want to be taking hits to their def. If you want to deal with B.Lyn, I suggest a manakete unless you want to put bowbreaker on Sanaki, but even then it's quite risky because Sanaki will not survive if B.Lyn initiates with a brave bow and you're never going to outmaneuver that cavalière. Your candidates are therefore Fae, M.Grima, and F.Kana. M.Grima requires the least investment because he comes with DC and venegeful fighter. If you don't care about B.Lyn, then I recommend an axe because nobody else on your team targets def. Your candidates are therefore any green armour (except H.Henry), Hawkeye, Dorcas, Bartre, Libra, and possibly others. The lowest investment units are Hector and Dorcas, who come with DC. (Original Hector also comes with QR on his weapon.) If mobility becomes an issue, you can use armoured boots or the guidance seal.

Here's how I would set it up:
Atk tactic: you might have to do without if Maribelle is stacking savage blows. I don't think you will have enough C-slots.
Spd tactic on your tank if he's slow (most of the axes are; M.Grima and Fae may or may not be depending on the build; F.Kana is not slow.)
Def tactic on either mage (not SS Camilla if she's using a blade tome or guidance seal)
Res tactic probably on SS Camilla, because Sanaki probably wants to receive it and Camilla's expecting to focus on offense.