You are required to report income when you have constructively received it. Since the bitcoin is yours every 4 hours to do as you please with no strings attached, you would have to determine the USD value of each of these payments, not the USD value when you took it out of the Nicehash account in lump sums into your own wallet. Sorry.
This would be classified as self-employment income. You do not need an LLC or form any type of business entity to report it as such. Some people do have a business bank account, form a business entity, get business credit cards, and keep the business's books separate from their own personal records. This is as a way to justify to the IRS that it is a legitimate business if questioned, and to provide a layer of protection for yourself. You are only required to get an EIN if you start making payments to employees or contractors.
Schedule C would be used to report this income. The gain or loss between when you received the bitcoin for your work and when you sold it would be recorded on Schedule D.
The foreign income question is a sticky one. Under current law, cryptocurrency is considered property and not currency. Therefore, it would not count as foreign income. The laws regarding cryptocurrency are evolving and it is possible this could change. See section 4 question 2 of this IRS notice and see this IRS page for more guidance relating to cryptocurrency.
