I agree with the others who have pointed out that you're already successful, don't break it!
That said, don't even consider HR as your first hire. Not even for a second. Their role is to police contracts and resolve issues. You won't have that until you have more people.
Get someone who wants to do the stuff you are tired of doing.
I really don't want to criticize the OP, but as an observation, the question reveals such a deep level of naivety about how to run a company that it bodes very poorly for the transition of this company to same-but-multiple-time-bigger-and-more-profitable.
Step One: talk to a local temp-to-perm agency about computer literate clerical staff or a personal assistant. This lets you defer ALL the HR/payroll/tax issues until much later.
If you can successfully outsource a non-core function, then do so. HR is one of those things that can be successfully outsourced particularly at the small scale.
The only maybe gotcha with outsourcing the HR function is that, while you can outsource the routine tasks (issuing payslips), you can not outsource to an outside firm the legal obligations surrounding employee contracts, employment law, obligations to pay correct payroll taxes, etc.
If you go the route of outsourcing HR, you may wish to consider investing a bit in HR consulting with the aim of educating yourself about employment law in your legal jurisdiction.
That said, don't even consider HR as your first hire. Not even for a second. Their role is to police contracts and resolve issues. You won't have that until you have more people.
Get someone who wants to do the stuff you are tired of doing.