A whole lot of those errors are due to a pretty sloppy coding error (not you -- I'm assuming it was in the theme) in this line of code -- which looks like it is in the header.php file:
This theme uses the 'site-color' picked in the theme-options page to set many different color values throughout the theme. These are all displayed below. If you would like another element to also use this color, add it to the corresponding lists below (background-color, color etc) or create your own! Remember to echo the color variable by using 'echo $ping_settings['site_color'];' within PHP brackets
the problem is all the hyphens in the last line -- HTML comments can't be closed that way. So you would need to simply remove all the hyphens except the very last two - so it would look like this:
Some of the other errors are not really a big problem. But the ones you need to track down are the extra or open or missing or stray tags -- those can cause problmes like you are having. Errors can be in the content (often) or sometimes in the php files. You have to look at the validator results at where the error is and then find that code in the site.
If you want to hire someone, it's probably not that a big job, but I can't guess at cost (partly because that's against the forum rules) and it is also impossible to know what kind of problems might be involved -- you can post a listing on this page:
But really, this is the kind of thing you probably want to learn how to do if you are going to have a site -- it's not that hard once you start learning it...