Tim Hunt

You do not want to set prohibit on all capabilties.

I think you should learn more about how Moodle's roles system works before starting to define completely custom roles.

Start with the standard roles.

If you are just getting HTTP 500 errors, turn on Debugging while you try to understand the problem, to get more info.

If everything is that slow, something is wrong somewehre with your infrastructure. Some things to check:

What is your Moodle caching setup?

Is there anything in your database server logs? (In particular, configure your database to log slow queries.)

If queries are being slow, then try doing whatever you need to do on MarialDB to get it to re-analyse each table. (On Postgres it would be VACUUM ANALYSE.)

I agree, and have done for a year: MDL-79268.

It should indeed be hidden.

Are there any JavaScript errors in the browser console?

Are you using a custom Moodle theme? If so, try testing with the standard Moodle theme, to see if that makes a difference.

I suspect you are missing the get_expected_data() method in your question class. (Important to also implement is_same_response.)

If you have that, then the core of the question engine will handle saving the responses for you.