Surely you can just outsource customer service to an offshore provider that is (a) cheaper, and (b) just a company that invoices you for their time (i.e. not your employee therefore not directly owed benefits taxes etc by you)?
I haven't looked into it, so I don't know exactly what price range is involved (and I don't know if it's a price that one could justify, depending on the exact income involved in your side project - but let's assume it's a fairly modest income), and I don't have any names to recommend. But from what I've heard, Philippines is the go-to for this sort of work these days (not that it's the only country, there are other options).
Outsourcing, or even part-time contracting, is a totally valid option. The main reason I want to invest in in-house customer service is that I see the role as more than just customer service, but also as a means to build community.
I think it is natural to see customer service in some industries as the kind of thing that gets tucked away into a call center or similar type of industrialized or factory-line like situation. However, I have seen the result when the customer service team is embedded within (or at least closely adjacent to) the development team.
Often these roles are more like "customer success" and they border on account management in many cases. They are part community building, part moderation, part customer training, part evangelism, part technical support.
So this wouldn't be a role in the vein of "answer X tickets in Y amount of time" but rather a much wider remit of ensuring overall community happiness by engaging in forums, answering questions and escalating technical problems, contributing to FAQs, etc.
My feeling is that trying to fill that kind of role with temporary workers, especially ones that are managed by some other company, would mostly defeat that purpose.
I haven't looked into it, so I don't know exactly what price range is involved (and I don't know if it's a price that one could justify, depending on the exact income involved in your side project - but let's assume it's a fairly modest income), and I don't have any names to recommend. But from what I've heard, Philippines is the go-to for this sort of work these days (not that it's the only country, there are other options).