Hi @Learning4me ,
You may have a look https://experienceleague.adobe.com/en/docs/experience-manager-core-components/using/developing/custo...
1. In the HTL, do I need to include only the new fields that I have added in the dialog?
Yes, we have to override the required html file as well and place the new fields in HTL where ever you want to display in component.
2. I should also update the Sling model to accommodate these new fields.?
Yes, if you need OOTB field(or methods(getters)) you can simply return the same with help of delegate and write your own getters(methods) for custom fields in extended Sling Model
Please have a look on how to extends(override) sling model https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/enhancing-image-component/...
3. And also how can I implement custom styles for the fields values, since most of the values are from slingSuperType ?
We can change the html structure and css classes as per you need in the overridden html file in our component, and need to write css/js in clientlibs (ui.frontend)
Note:- Do these changes in overridden component in apps/project/component not in OOTB core component
Below references are good to go through if you are new to this concept
https://aemgeeks.com/aem-tutorials/overlay-vs-override-in-aem-as-cloud-service/
https://aemsimplifiedbynikhil.wordpress.com/2023/02/27/extending-core-components-model-and-creating-...
https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/extend-aem-ootb-core-list-...
Thanks