I don't think you need the !important.
For the standard paragraph, I use...
p {
display: block;
margin-top: 0;
margin-bottom: 0;
text-indent: 1em;
}
Then, for those paragraphs that don't use an indent I use...
.noindent {
text-indent: 0;
}
Also, you need to check the css for the <body> tag in case it needs tweaking.
Great that it is slowly coming together for you. What ereader are you using?
And if it helps, here is my css in full which I adjust as needed on a per-book basis. Might give you some pointers...
https://paste.kodi.tv/rovohaxatu