ASK HN: How to Hire for Remote Work, Full-Time vs. Contract?

We have about 10 US-based team members working for us as contractors, sending them 1099. The team is all remote, located in different parts of USA. We grow fast and need to make sure we do not break any law. We wanted to start hiring full time, but heard about nightmares of hiring when team is spread through different states.

How companies approach this issue? Is it possible to have people working 160+/hrs per month as contractors? How hard / beneficial is to hire full-time? Do we need dedicated HR/lawyer, or using a solution like gusto is enough?

What is the real cost of hiring an employee? If a base salary is $5k, how much will go for taxes? Do we need to provide an insurance? What about overtime? We cannot afford to pay 1.5 rate, we rather offer some bonuses. Can we state in the agreement we can fire anytime without providing a reason? Can you recommend some solid, not crazy expensive law/HR firm?

Thanks,