I made an Excel to track how many more rings I need to fully skill up my heroes. I’ve shared it here in case you want to try it out
How to use it
- For each hero, and for each star level, enter the current skill selection (M is for the middle choice, U for Up, D for Down) in the first table, and it will calculate how much you’ve invested in the Skill trees
- In H33 enter the available free rings, so it can calculate the total available rings
- In the lower table, enter the configuration you want to have, and it will calculate how much you need for that, and the shortfall compared to your current inventory
Note - the link is open for anyone to edit, so your changes can be over-written by someone else, and it can be messy if multiple people try to edit it at the same time 
. If you have Excel on your computer you should be able to download a copy and work on that instead.