In regards to updating, I wouldn't suggest just updating some of the files based on modified dates. Sometimes the theme folders are changed (structure, where files are located etc) as well so then when we look to see if the version number is correct in the CSS, we might not be able to actually diagnose a problem.
As long as your modifications to the theme are in the Quick CSS or the custom.css, completely overwriting the theme folder won't cause any changes in your site. If you make changes to the core files you will need to look over the version log to see if any changes were done to those pages that will cause a conflict. If so, you will need to re-add those changes to the php, css or js files.
You can always look at the version.rtf located in the zip file you download from themeforest. Kriesi puts notes on which version you just downloaded and the various changes for each version.
Re: Interesting links - Just add any widget to the Footer - column 1 widget area in your Widgets admin. The default footer text/information is only there until you replace it with your own widgets.
Re: Text under portfolio - I don't know of an non-complicated way to move the text below the image for the portfolio inline view. Its a bit out of the scope support can do.
Re: RSS Feed - That is your wordpress RSS feed. You can use a service like feedburner to allow easy subscription to your content: See http://support.google.com/feedburner/bin/answer.py?hl=en&answer=79408
You can disable it from being viewed by adding the following to your Quick CSS or custom.css file:
I'm not sure what you mean about the portfolio images.
Please make future questions in a new thread, its very difficult to keep track of questions in older posts that span pages.