Is it stupid to hire employees as a sole proprietor?

First of all, I would get incorporated to protect your personal assets. But either way, if you can afford to hire an employee, understand employment and tax laws, and have the workload to justify the added expense, by all means hire someone.

No ... if you can't do all the work yourself, you hire an employee.

employees are capable of becoming sole proprietors but sole proprietor's hire employees

You are way too awesome to ever be stupid. Without knowing much about the topic... I am sure your amazingness will prevail!

A sole proprietor can hire employees.
But employees can't replace the sole proprietor.
All that you could do is to give a power of attorney to trusted employees at Managerial levels so that they could affix their signatures on your behalf using the mandate given by you which will be legally binding on you.
But be careful about giving more powers than necessary - otherwise it could turn a stupid move. The sole proprietor might end up loosing his business to his power holder!

It IS risky. Incorporation is all about protecting the owner legally. You'd be smart to take advantage of that.