Rebuild website + SEO + customer data collection

Hello. We have a rather outdated Wordpress website (porta-gym.co.uk) and are looking to hire someone (potentially on a long-term/regular basis) to either upgrade the existing website (e.g. update the plugins and PHP etc to be aligned to modern standards) or rebuild it completely (not necessarily in Wordpress) if deemed more appropriate. Once that first phase is done, we want the website to have Google Analytics and customer data collection functionalities and also to perform well in search engines i.e. some SEO work. Looking to get proposals that outline the proposed schedule of work and the costs. Fairly open-minded about how to improve the website and am looking forward to hearing your ideas. Thanks!