Developer needed for Open Journal Systems(OJS) website update

We are looking for a web developer fluent in Open Journal Systems (OJS) to update our academic journal website to the most recent version of OJS. The website was designed with OJS about 7 years ago, and our web developer at the time made many custom patches that, it is my understanding, make a simple update impossible. We want to update versions because the older version is losing functionality as it continues to be outmoded, but we also don't want to lose our custom features in the update. The website is www.marketsandmorality.com. Current problems include: - Article pdfs don't display in Firefox. - The website is no longer communicating with Paypal properly. Subscriptions can be purchased, but they are not marked as Active anymore when they are, and new subscription emails are no longer sent. - We also want to acquire and integrate DOIs for all our articles, but it is my understanding this is impossible with the current version of OJS the website uses. --