WordPress QA & WooCommerce Bugfixing

My live WordPress site needs a thorough health-check followed by rapid fixes. I want every corner of the installation—theme, child theme tweaks, core files and the full WooCommerce stack—to run flawlessly, especially the payment gateway, which is mission-critical for me... (Budget: €1500 - €3000 EUR, Jobs: CSS, Debugging, GTmetrix, JavaScript, PHP, Website Optimization, WooCommerce, WordPress)