Going on APKmirror and downloading it from there always worked for me. If one of those download links doesn't work try the other, and if you have any problems afterward look at IDC_SAO's video on it if you haven't yet.
Go the the FEH Google Play page, scroll to the bottom to the "Additional Information" section, and under "Permissions" click "View details".
So we won't find out until 6/7 - 6/8, but it still isn't getting implemented until 6/12.
From the way they use "deploy(ed)" in official text,
https://fire-emblem-heroes.com/en/topics/
You can deploy up to 20 Heroes in these battles—and you can even recruit allies from your friends for these fights. (Rival Domains)
Please note that duplicate Heroes cannot be deployed. (Even if the correct blessing has been conferred, only one of each Hero can be deployed at a time.) (Blessed Gardens)
Example: During the Water season, a Hero with a Water blessing deployed with Fjorm: Princess of Ice will get HP+3 and Spd+3.
Deploy pairs of Heroes into a battle with enemies level 35 or higher to build their Support Rank from C to S. (Ally Support)
Also, once you deploy a Hero, you cannot use them again until you've made it to the end of the Arena...or a game over screen. (Arena Assault)
Once captured, they cannot be deployed again until the challenge ends. Clear this mode to earn Sacred Seals and Orbs! (Squad Assault)
If a Hero falls in battle, they can’t be redeployed until the end of the challenge, so be careful. (Tempest Trials)
As in use/play as, I can't help but think it'll be a max of +28 as patoente concluded to. So 56 trained + blessed units (14 per element = 3.5 teams each element), including your 3 high-scoring Arena cores for 3/4 elemental seasons (especially since Wind's Lyn and Gunnthra are BSTlets). Certainly more demanding than the minimum 28 to just clear it prior, but AA's scores of 5278 Max / 5212 Top 1000 / 5136 Top 3000 / 5082 Top 5000 would get more leeway?
I wasn't around for the drama. Was it that datamining is a form of reverse engineering against the Terms of Use so mods took action on posting datamined contents? Are we not allowed to post on how to datamine?
My post on how to play on an emulator got deleted for supposedly violating the Terms of Use when it did not.
I like Soren because he has options. If you want to run a blade tome, he can, albeit not as well as Nino of course, but still pretty good, or you can set him up with his prf. I did an analysis on Soren vs Nino in a podcast format, you can check it out and see if it helps.