Personally I would keep on with a couple more 4* heroes before starting the time and resource sink that 5* heroes are (not even mentioning how expensive they are in materials)
I spell it out more in this post here:
So in saying that I would probably do:
Blue - Sonya costume & Triton (maybe Valeria too…?) (Kiril too if you get him)
Red - Colen for sure. BT 2 next then Grazul and then back to gormek 2
Green - Melendor & Brianne costume. Then Gaderius.
Purple - Tiburtus & then grimble
Yellow - Li Xiu 2 then Joon. If you get Wu Kong max him ASAP
TC20 is a great free resource. From it you can train 5*, 4* and 3* vanilla (season 1) heroes.
Essentially gives you a chance at summoning any hero available in the normal Epic Hero
Summon Portal.
Odds are approximately 5% for a 5*, 25% for a 4* and 70% for a 3* hero (approx. From memory).
Cost is 100 recruits and about 300k food. Takes 2 days to cook a training.