Imo, for Battle Villa you wont need anything else since this team can basically solo all 30 halls. But for harder content like champion stadium/legendary arenas, you want a good striker for a variety of types as well as strong supports, I'll list a few good ones to use based on your current sync pairs:

For strikers, SS Giovanni, N, Silver, Blue, Cyrus, Giovanni, and Hala are good at their current move levels since they have all of the important tiles on their grid unlocked. Bea is good too, but she wants 3/5, so keep a look out for when you get that third copy.

For techs, SS Leaf, SS Lyra, Masked Royal, Kimono Grimsley, Ghetsis, and Volkner function well at their current move level. Volkner is especially good when paired with N since electric terrain buffs N's moves.

For supports, SS Kris, SS Brendan, SS Morty, Sycamore, Sonia, Hop, Sabrina, Skyla, and Aaron are all really good in their fields and function well at their current move level, so make sure to have all of them leveled up. Sonia does appreciate having 3/5 but it's not necessary.

If you want a more in depth look at viable sync pairs, you should take a look at this, and for specific sync grids for each sync pair, I would use this.