First of all, Format
>Character
is direct formatting. This means it has a local effect and you don’t control it centrally, which is essential when you work with a sophisticated document and layout.
Your kerning adjustment should be set in a paragraph style, so that all similar paragraphs share the same configuration.
Theoretically, you don’t need to adjust indents because kerning acts upon pairs of characters to “admit” more words in a line. So, you should have the same number of words and justification will compensate for “irregularities”.
I emphasised words to insist upon the most frequent case where hyphenation is not enabled. If it is enabled, you will indeed see differences as syllables may be pushed into lines. Equally, kerning makes sense only with justification because paragraph contents is flushed on limits at both sides. Without justification, right side is jagged and it is not really important whether letters are closer to each other or not.
Do you really need more than one decimal in the Character spacing parameter?
I am not sure about that. 1 pt = 1/72" ~ 0,35 mm. 0.1 pt is 0.035 mm or 35µm; this is really small. In a 15cm-wide paragraph at 12pt character size, there are ~90 characters. 0.1pt leads to difference of ~3mm, i.e. 1/50 the line width or 2-3 characters.
If hyphenation is not enabled, only words like ‘a’, ‘of’ or ‘the’ are susceptible to slip into the current line from the next. And I don’t take into consideration the space before the word, which probably rules out 3-letter words like “the”.
In this case, some cheating on paragraph indents should fix the problem. Don’t modify page margins as they are global to all paragraph styles, notably headings. Instead, set paragraph indents to a practically unnoticeable 0.1 mm both on left (Before text) and right (After text), or only on right 0.1-0.2 mm in order to keep headings and text rigorously aligned.