A self-directed individual retirement account is an individual retirement account (IRA), provided by some financial institutions in the United States, which allows alternative investments for retirement savings. Some examples of these alternative investments are: real estate, private mortgages, private company stock, oil and gas limited partnerships, precious metals, horses and livestock, and intellectual property.  The complexity of the rules for self-directed IRA's  prompted the SEC to issue a public notice in 2011  against an increased risk of fraud.
In 2019, the maximum self-directed IRA and self-directed Roth IRA contribution was $6,000 or $7,000 if over the age of 50. 
Internal Revenue Service (IRS) regulations require that a qualified trustee, or custodian, hold IRA assets on behalf of the IRA owner. The trustee/custodian provides custody of the assets, processes all transactions, maintains other records pertaining to them, files required IRS reports, issues client statements, helps clients understand the rules and regulations pertaining to certain prohibited transactions, and performs other administrative duties on behalf of the self-directed IRA owner.
The account owner for all IRAs chooses among the investment options allowed by the IRA custodian. For regular IRAs these options usually include stocks, bonds, and mutual funds, but with a self-directed IRA, the term "self-directed" refers to the significantly broader range of alternative investments available to the account owner. IRA custodians are allowed to restrict the types of assets they will handle in addition to Internal Revenue Code (IRC) restrictions. 
From what I have seen, setting up an S-D IRA can have fairly high startup costs, that can include the creation of an LLC, as well as other setup charges, as well as annual fees, over and above any transaction charges when buying or selling a crypto. I have decided that the cost and complexity makes it a no-go for me.