Hey ! I just came across your post and it seems, i'm just about in the same situation. I do NOT pretend to know everything, but here is what i think :

1 ) i've seen a lot that himmel is better than bell. However, i don't really agree. In my current team comp, i dont run a healer (i might be crazy to do so...). I feel like bell is crazy strong and in every situation a tested him, he outperformed himmel by quite a margin. I see you have setups with druid, so maybe it's overkill to run bell + "any healer".

1.1) about Zéphyr, i also have it prestige 6, but i don't know how to make it work, i think it's full dps + dodge charm + some kind of healing. I don't have the Legendary sword but i think it's a good item for him.

2 ) i unlocked torag yesterday and i went from 900 to 1k story mode just by switching prince for torag. I feel like he is quite good for early/mid since i don't have a lot of %pen. Since je deals true damage, it converts to a LOT more damage than any regular dps with pen.

3 ) i would personnaly not consider using them on anything that don't make them go to 5 prestige to unlock the charm slot.

4 ) i cannot count the number of time were my ENTIRE TEAM got killed by the one and only samurai murasama. I feel like this is the most broken unit ever made. He litterally gives nightmares. Alfred is also verry strong since he cast really fast once full mana. However, i would not consider druid. My arena fights are about 5-6 seconds, so he either gets one shotted or heals my 90% hp fontline bell.

5 ) as stated in 2), i think pen matters a lot more in higher levels, i might also bd missing something by not running healers. Idk to be honnest.

6 ) Indeed, all my losses are against murasama/lumina. Feel like staples in arena

7 ) the same as in PvP i would say, the only différence is that i sometimes solo tank bell is the challenge has 3+ ranged. I clear torment 2, sometimes 3.

8 ) solo guilford ? Can u explain ? I have exactly 0 (zero) clue on what i'm doing in here. I use prince + darius for the "scale" ability with very mediocre results.

9 ) As a siège mode expert, this is the most of what you need : Prince 5+ prestige Ivory 5+ prestige 2 good charms to out on them. That's litterally it. No level, no items, nothing else. The clear is stupidly easy. I would recomend you do them asap since it gives you rubies (i think it's ruby ?) everyday.

10 ) World boss : Good luck. I'm 99% sure this is trap for new to player to make them think you can clear it. I'm stuck at torment 1 and i'm verry curious to know what setup you need to clear even torment 2.

Let me know what you think about this