Customize front page form

1. you can hide the fields using adverts_form_load filter or by using the Custom Fields extension https://wpadverts.com/extensions/custom-fields/

The code below will hide the fields in the [adverts_add] you can add it in your theme functions.php file

add_filter( "adverts_form_load", "customize_adverts_add" );
function customize_adverts_add( $form ) {
  if( $form['name'] != "advert" ) {
    return $form;
  }
  foreach( $form["field"] as $key => $field ) {
    if( in_array( $field["name"], array( "adverts_price", "adverts_location", "post_content" ) ) ) {
        unset( $form["field"][$key] );
    }
  }
  return $form;
}

2. similarly as above you can limit the file uploads to just one file by using the Custom Fields extension or the Limit File Uploads snippet https://github.com/simpliko/wpadverts-snippets/blob/master/limit-file-uploads/limit-file-uploads.php

3. this most likely can be hidden with a CSS snippet but you would need to paste a link to one of your Ad details pages as the CSS code which will do it varies from theme to theme.

I understand you would like to remove the part “By Startup Botswana October 8, 2018”?

If so then please go to wp-admin / Appearance / Customize / Additional CSS panel and add there the code below

article.classified .post-metadata {
    display: none !important;
}