just to to the creation circle to see what is need to turn them into 6 stars for each hero but overall you need 2 of the same hero in 5* form, then a specfic 5* of the same element then 3 random 5* of the same element.
7 star is 4 5* hero of the same element,
8* is 1 6* of the same element and 3 5* of the same element.
9 star is 1 of the same hero, 1 6*, 2 5* all of the same element.
10 star is 2 of the same hero ,1 6* star same element, 1 9* of any element.
Best advice I can give is don't worry about progess it will be slow, just play the events as best you can and just wait. I have been stuck with 3 10* for months not not moved on the tower, clear the same level in island and Dungeon and finish around the same PVP rank. I have 6 heroes waiting at 9 star just hoping for some luck on drops. Then when you get a full team of 10 star you need to start trying to make teams for specific functions. Never ending grind