Hey Ben,
1) I do not know how to perform a layout override or edit CSS but I am trying to learn. I am trying to edit the file public_html/components/com_hotspots/views/form/tmpl/form.php to remove some of the form entry fields -- is this correct?
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docs.joomla.org/Layout_Overrides_in_Joomla
if you are doing changes to CSS what I do concider a standard right now is to have a custom.css file (provided by most templates) and write your CSS modifications there.
by using layout overrides and puting your css overrides in the custom.css file you ensure that updates to the extension won't override your chagnes.
2. Sometimes the language manager doesn't find the entries, despite them being there (it has something to do with the location where the language manager looks for the string - frontend or backend) With out component we have some strings in the backend and some in the frontend. We merge both files in the frontend and backend so it's fine. So just create a language override and enter your new strings. Even if the language override component doesn't find the strings, they should still work.
Regards,
Daniel