What should I have on my team?

Honestly? Olivia.

You already have all of the SS-tier heroes there already and its hard to imagine an opposition that a 2x turn from any of your big 3 can't demolish. Basic setup would be to frontline with Hector, and give Linde the extra action to fire again while healing Hector twice in the process.

As Linde already covers your blue unit, Olivia may actually have a edge over Azura in this instance as:
A) The damage aura might just put Takumi over the edge to OHKO a few casters and
B) You get better odds in a few marginal cases (a team with Cecilia, a team of multiple Hectors) where you'd be in trouble without a red unit otherwise.

I see a weakness to enemy Hectors for Linde and Takumi. Tiki (Y) would work fantastically for that situation and is a great unit overall. Any strong red unit that can tank a hit from Hector can push past his 80% follow-up Armads passive and open the way for your Linde to kill him. I like using Eirika with Linde and Takumi because of the +4 Spd and +4 Atk buffs to adjacent allies she gives, as well as solid stats and utility to back her up. While Olivia would certainly give your team a big damage spike through attacking twice with Linde/Takumi, Tiki (Y) brings a small amount of healing and her insane damage as well. Eirika's buffs also compliment Linde giving her a massive 43-46 (pref) Spd that will help vs fast green units (Nino).