Validation issues with numeric entry fields

Hi all

Thank you for your time and POV. I need this quiz to work, but I encounter some issues in the process:

1) Learner gives a value between 0 and 10 to statements (+10 statements per slide) in a numeric entry field.
2) The score is then transfered to the next slide and continues with the rest of the statements.
3) After ending the assignment, the score of both are divided to get an average per group (specific var per group) and the results go as average to a results slide.

As simple as it may sound, I'm getting a lot of issues, mostly related to user error handling. For some I found a workaround, for others, well, I'm clueless...

A. User forgets to enter a value or is using other values (>10).
B. User wants to change a given value after input, but it should not add to the sum.
C. A layer should be shown that informs them on erroneous input, but since '0' is also a valid value, it affects some standard trigger behavior we could use.

So, I use an edit btn to let them change an already entered value in the same slide. The edit resets the scoring to '0'. Therefore, a validation btn is adding the (existing and changed) values again (add value after lost focus not possible because it adds to the sum).

After succesfull validation (if 'between x and y'), I block the numeric entries via a shape, put a next button over the validate btn to proceed to the next part/slide of the assignment. There the same mechanisms apply.

For the issues now
- I am unable to give them a warning when failing to enter the values correctly.('not between' or 'blanc' as a trigger is not possible)
- When editing the input on the 2nd slide, I revert to the former slide (because 'sum'), but the Next btn should be hidden again.
- There's not much of feedback when validating, because of the restrictions/issues mentioned.
- If 'validate' finds an input error, it's not clear that the learner should hit 'edit'. I don't see how to hide the 'validate' after error.

I spend more than 1 long day to build this, the workarounds and such and testing everything, but it's still lacks the most evident uses :-). So I guess I'm totally derailed here to get this working. Every workaround brings up new impossibilities.

I am very early in the process of designing courses in Storyline and not a dev, so alternative workarounds/processes/tips would be gold. So, help please :-)

I created/translated a simplified example for you to look into.

Many thanks!