Don't hire until you're absolutely ready to hire. Building a team to run an imaginary business just burns time and money.
You know you need someone to join your team when...
1. You, or someone on your team, is underwater and the tasks hitting the floor are holding the business back.
2. You don't have anyone on the team who is good enough to complete an essential and immediate task at the level of quality/effectiveness needed.
For example, don't hire a sales person unless you have a product to sell - and you've personally figured out how to sell it with the first few sales. Don't hire a growth marketer until you have a self-serve product ready to onboard and retain users. Don't hire a community manager until you have a product worth building a community around.
Noticing a trend? Build a PRODUCT that people want to use and is ready to scale before scaling your team.