Module development and code questions

I have a simple jquery call in my custom module to dynamically change the css depending on the visitor. The first uses find() of a class in a header and it seems to work fine. Now, I need to find another set of elements in a sidebar but it's not working. When I first was watching it move through my function I saw that the sidebar was processed well after my script had run. That leads me to think to use .once() for both calls but the second ends up changing the sidebar height to 1px.

I want to store some data that is related to a node and trying to figure out the best way of doing it. For example, I send emails related to a node and I want to save details such as:

• To Email address
• Cc Email Addresses
• Date sent
• User
• Email type
• Other chosen email options etc

In the past I would use Paragraphs to have an unlimited field but this will, over time, grow to have a lot of entries. I'm also using Revisions on the node so I think this will slow everything down when saving the node.

I have a node that has a Paragraph field. It has around 80 Paragraphs referenced to it. When I save the node programmatically it's very slow. It seems like the slow down is happening in the preSave() of the field. I'm wondering if every referenced Paragraph is being loaded when the node is being saved?

Could it just be bad design by myself that I created a node that has a field with 80+ Paragraphs referenced to it? Or is it legitimate to do it this way?

I should add that the node uses revisions.

I have this route that is suppose to render a block and two view blocks and then display them in a modal.

Originally, I had this route created in the Pages section of Structure, but then decided to create it in my module using this tutorial

You can open any page in a modal from by making the link like:

<a class="use-ajax" data-dialog-type="modal" data-dialog-options='{"dialogClass": "my-modal"}' href="my/custom/page">
  {{ 'Open Modal'|t }}
</a>

You can create an endpoint that uses a controller method that responds by opening a modal like:

Hello, I would like to modify the layout of the contact form and just add an image. Unfortunately, I can't do it. My block is well created, there are two options, I select both and in custom display settings, I created a custom mode view. 
I can't do it. I have just tested layout builder for articles for example and there no problem but for the contact form I can't do it. I followed what is written in the layout builder documentation, however.
Does anyone have an idea ?
Thank you very much for your help.