WordPress Bug Fixing

My WordPress installation is showing error messages on both the public-facing pages and inside the admin dashboard. The goal is to trace the source of these notices or fatal errors, apply clean fixes (not quick suppressions), and leave the site running smoothly again without introducing new issues... (Budget: $10 - $30 USD, Jobs: Debugging, HTML, MySQL, PHP, Web Design, Web Development, Website Optimization, WordPress, WordPress Design, WordPress Plugin)