Forget about using <br/>. You need to define some classes in your stylesheet, with suitable values for text-indent and margin-top. This should do. Use <p class="p1"> for the first paragraph of a block, just <p> for subsequent paragraphs.
p {margin:0; text-indent:1.3em;}
.p1 {margin-top:1em;text-indent:0;}
<body>
<h1>Title</h1>
<p class="p1">First paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent</p>
<p>Subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above.</p>
<p>Short paragraph with same settings.</p>
<p>Another short paragraph with same settings.</p>
<p>Subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above subsequent paragraph with no indent or space above.</p>
<p class="p1">First paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent first paragraph with space above and indent.</p>
</body>