My advice:
Stop working on 5* heroes for the moment (once you get them to the end of their current ascension tier… so finish Kingston & marj to 4/80 & stop Kage at 3-70)
Reason being that they are a) time consuming and b) expensive…
Until you have a firm foundation of 4* heroes maxed, you’ll be suffering in terms of overall depth & also in your usefulness in things like wars, titans, raiding etc…
My advice would be to work on 4-star heroes ONLY until you have 3-4 maxed rainbow teams of 4-star heroes.
So with that being said, I would focus on:
Red - Colen then Kelile to 4/70
Blue - Sonya then Triton then Boril to 4/70
Green - Caedmon then Melendor then Gaderius to 4/70
Yellow - Li Xiu then Chao then Hu Tao to 4/70. If you get Wu Kong, bump him to the top of the yellow list.
Purple - Rigard then Tiburtus then Cheshire Cat then Cyprian to 4/70
ONLY Once you got the 4x 4* maxed in each colour, would I suggest working on 5* heroes again:
Red - Go marj finished (hopefully) so can work on Grazul.
Blue - Vela is the better of your two options. Perseus is a pretty rubbish HotM & Sniper.
Green - Already maxed Kingston so this will take you a while to get to 
Also have no options.
Yellow - Vivica is probably the better of the two you have. Then Leo after if you get a second set of darts.
Purple - Finish Kage. Definitely the best one you got available.