ShortMath

Hi,
How can I customize the symbol menu to my needs?

No, it isn't.ShortMath is not designed for autograding, but rather for in-class discussion where the answer is debated rather than cast in the digital stone.
We are working on an adaptation of STACK, using the same front-end as ShortMath with the advanced auto-grading backend of STACK. If you could send me a complete sample question with desired grading behaviour, we can have a look to see if it can be implemented easily in STACK. If you want to try for yourself, the current alpha version is here: https://github.com/KQMATH/moodle-qtype_stack It will take time before we see it incorporated in the official STACK because it depends on multiple refactoring exercises.
If the student answers with only a single floating point number, you do not need the maths editor. I would suggest to use calculated instead, or possibly, STACK. They allow you to set tolerance freely.

Is it possible to allow for a range of values in a constant? For example 2.1 +/- 0.1

We are working on an extension of STACK, using the same GUI editor for the answer. We are working together with the STACK development team on this. Hopefully, STACK will provide what you want in the future. Unfortunately, there are several challenges to resolve before it all works together, so I am unable to give a time frame for the project.

I love this plugin, the interfase is amazing, but i think, i would be better if the plugin has an option to add random parameters for the constants of the expressions.

Please see CONTRIB-7462 for a summary of the review status on this plugin - thanks!

Approval issue created: CONTRIB-7462