Module development and code questions

Hello

I'm new to progamming and working with Drupal. So I was interested in  making a site with an audio recorder that sends the recorded files to a API and get the results back. I found out that H5P Offers a Audio Recorder and I would like to leanr/understand:

• How can I add an extra Button?
• In wich file can I do it?

If someone could help me with that, I would appreciate it a lot.

Link for setting up H5P: https://h5p.org/documentation/setup/drupal8

A field widget was implemented to render an input with a corresponding datalist. The widget works just fine when

selected in adjust form fields through the backend. But I just can't get the widget to work in a render array.

In drupal 8, I plan to create a custom module that will expose an API. This API will drop a cookie on the browser to recognize the application user. Would there be any issues with caching in this solution? 

I am using Drupal 8 Commerce. Need to integrate inventory system. We have proposed to use https://www.tradegecko.com/

Anyone having integrations with this? Or better inventory management software that supports Drupal

I have a custom Menu Link that I would only like to appear on specific pages. These pages have a parameter being passed through via entity upcasting. It also has a custom access check.

I have tried having a check in the IsEnabled but if there are two pages consecutively that shouldn't have it enabled, it won't appear on pages that it should. I have also attempted to use the updateLink function, but to no prevail.

I am relatively new to Drupal so my apologies if more information is needed. If requested, I will try to upload more information.

I have created a custom block though Drupal Admin mentioning page restrictions (to show only on listed pages) and have included this block programmatically in a node twig file but, this block shows up in all the node pages rather than only mentioned pages. How to restrict this block to display only on restricted pages through coding?

I have already restricted the pages in block (created through Admin interface) but the block is being displayed irrespective of it's page restriction on all node pages.