Hi,
I think you can limit the text in a post using SharePoint Designer:
1. Open the blog site in SPD and open the default.aspx page;
2. Locate the post list view, and "Convert to XSLT Data View";
3. Look for the body text, you will see the code like this: <xsl:value-of select="@Body"/>;
4. Replace the code to this <xsl:value-of select="substring(@Body,1,62+m)"/> (“m” is the count of the characters you want to display in the post). If the code like this <xsl:value-of select="substring(@Body,1,72)"/> , it will display 10 characters in the default page.
If you want to set “read more” link, I think you should use JavaScript to set the button.
Hope it helps.
Xue-Mei Chang