Cannot adjust the excerpt length even with plugin or code

edit index.php; find:

<?php $truncateContent = truncate::doTruncate(strip_tags(get_the_content(), '<p><a><br/>'), 300, '.', '...'); ?>
             <p class="desc"><?php echo $truncateContent; ?></p>

– custome the excerpt length

the length is determined by the number 300 – increase that.

– add read more… text
– make read more…text link to the full post

for example, change the posted code section to:

<?php the_post_thumbnail(); ?>
             <?php $truncateContent = truncate::doTruncate(strip_tags(get_the_content(), '<p><a><br/>'), 300, '.', '...'); ?>
             <p class="desc"><?php echo $truncateContent; ?></p>
             <p class="readmore"><a href="<?php the_permalink(); ?>">read more ...</a></p>

– the thumbnail shows with the excerpt, thumbnail from the featured image of that post

the code for the thumbnail output is already in the above.
you might also need to add some code to functions.php; see http://codex.ww.wp.xz.cn/Post_Thumbnails

will possibly need additional formatting – please post a link to your site for suggestions; or use a tool such as Firebug http://getfirebug.com/ to investigate what you need to edit.

– The thumbnail does not show,

possibly caused by your character set (?) – it is maybe the best to start a new topic just for the thumbnail problem.

the other questions are related to the unique way your theme creates the excerpt, which also seems to be influenced by the ‘more tag’ if this exists in the post.

I personally would remove the code and use the_excerpt() instead;
you can then use all the instructions from http://codex.ww.wp.xz.cn/Function_Reference/the_excerpt for the ‘read more’ link etc;
the only thing is, you will not have links and linebreaks in the excerpt anymore.

the section I suggested earlier would then look like:

<?php the_post_thumbnail(); ?>

             <span class="desc"><?php the_excerpt(); ?></span>

If I need thee homepage to pull my custom excerpt which I add when I create/edit post, how can I do that.

as alsready suggested, use the function the_excerpt() in index.php instead of the original code from the plugin.

try to style the image by adding some styles to style.css;

example:

.attachment-post-thumbnail { float:left; margin-right: 10px; }
.post h2 { clear:both; }

the second style is needed to clear the next post title if a post is too short.