Samuel,
There are two kinds of SDIRAs. The kind I have is a "checkbook control" type, which I much prefer because once it is set up you don't have to go through the custodian to buy real estate or stocks or whatever. You just write a check and buy the investment as normal, but you have to know what you're doing or you'll get in trouble with the IRS. In particular, you must get educated on the "self-dealing" prohibition. For instance, buying a house with your SDIRA and then renting it to dear old mom or yourself or your kid would be examples of self-dealing. Also the only kind of loan that you are allowed to use when buying an asset with an SDIRA is a non-recourse loan, which is difficult to get. And then you have to pay taxes on the portion of your profits attributed to the loan.... as you can see it gets a little complicated.
I hired this firm (selfdirectedira.org) to set up an LLC in my state. That LLC is owned by my SDIRA, but I am the manager of the LLC. The LLC currently owns one rental house, a mortgage note paying 12% and a stock brokerage account at Fidelity.
This company (www.iraservices.com) is the custodian of my IRA . Their annual fees are a lot lower than some of the others, but they don't hold your hand or even give advice.
You probably should retain the services of a lawyer who specializes in this area (very few lawyers know anything at all about it). I signed up with this law firm (http://andersonadvisors.com) which has one or two lawyers who specialize in using SDIRAs for real estate investing. I pay a small monthly subscription (I think it's $35 for the "platinum membership") and am very satisfied with the occasional guidance they've given me.
I talk to a lot of people who are unsatisfied with their SDIRAs, but they all have expensive custodians who must approve every investment and by the time they get approval the deal opportunity is gone. They don't have the "checkbook control" type of SDIRA.