Skadi and Frigg are solid heroes to ascend, Hel is execllent, Vivica and Baldur are also good.
If you don’t have the resources needed for them to reach their 80th level you can still have them at 3.70 and not finding them underwhelming, just try to get their special skill maxed before hitting the ascension’s wall.
As first thing I would focus on your 4* heroes wich can go as far as 3.60 without requiring unfarmable materials to upgrade, a pair of healers for your everyday usage like Gullinbursti and Kiril can do the job very well.
At the same time try to level heroes that can equip a costume, they will be very useful for class trials, try to level as many heroes who decrease defenses or heals while increasing attack as possible.
Good job on ascending Caedmon, he is a solid hero 
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