4-5k a month is more than enough to make a hire. Think of it this way:
What is your time worth to you?
Would you rather work your ass off and make 5k, or have a sane workload, make 2k for a while, which then rises as you have adequate internal infrastructure to support growing sales and users?
It sounds like you have a good thing going, and I'd strongly recommend at looking to get another pair of hands involved - or close it down.