If you can’t ascend any of your heroes right now, I would focus on building all of your 4* to 60 first, then start on your 5* to 60 while you wait. Also, I would consider keeping some solid 3* to use during war, color-stacking and events. If you do keep 3*, I’d work on them after the 4*.
3* Worth Keeping:
Red: Nashgar, Rudolph, Hawkmoon, Azar, Namahage
Blue: Valen, Ulmer, Gunnar, Gato
Green: Belith, Berden, Brienne, Mnesseus
Yellow: Bane, Gan Ju, Kailani, Melia
Purple: Balthazar, Tyrum, Chochin, Gill-Ra
For your 4* (If you can fully ascend the first couple I list, I would):
Red: Wilbur first for events and titans, BT if you pull him, Kelile last
Blue: Grimm is the best 4* blue, Kiril if you pull him, then Sonya for dispel, Valeria last
Green: Hansel is the best 4* so him first, then Buddy because he’s also pretty amazing, then Caedmon if you pull him (or Melendor)
Yellow: Gretel is solid and you’re far with her, then I’d do Jackal next (great for purple Titans and tanks, but needs another yellow with him), Chao after (unless you pull Wu, he moves to the front of the line then).
Purple: I’d take Rigard before Sabina, then Tibs for Titans and events, then Sabina (unless it’ll be awhile til you get Sonya in the works, then I’d move Sabina ahead of Tibs, dispelling is important)
As for your 5*, they are all really good. I wouldn’t bother with them just yet- at least not until you have at least three fully leveled 4* in each color, and are close to having all of the necessary mats to ascend them.
Red: Red Hood is amazing, and Marjana is a solid sniper that’s a jack of all trades, both worth the mats.
Green: Lianna is the best of her class, and Evelyn will be great in a green stack and for Titans, both worth the mats.
Yellow: If you lack healers for war, I’d get Vivica in the works sooner, she’s the best healer in the game. Worth the mats.
Purple: Domitia dispels buffs, but at average mana it’s not as helpful as Caedmon or Sonya, but she does have her place. She’s one I maybe would wait on ascending, but she’s good.