I've never done a "self directed" IRA (yet). But I can tell you about my experience borrowing from my 401K. I have done this about 3xs.. first I would recommend asking if your plan manages loans? If so, this is a good thing, you can save money on these costs. Your company might have rules of when your money is vested (only vested money is available to barrow) and you can only barrow 50% of the money (from any IRA retirement fund I think). The new loan payment comes out of your pay check, payment with interest. Depending on the plan you can do up to 5yrs or a primary residence up to 10yr.
When your working with your lender let them know you will be borrowing against it. They will factor this into your ability to pay. Trick here, add a dependent on your taxes (since a house is considered a dependent). Or barrow your 401K to remodel your purchase.
Down side, if you quit or move on from this job then your balance is due. If you can't pay or don't pay then you will be taxed at an upwards of 30% on the balance due.
I'm a big fan of the 401K save up plan, I suggest putting in the maximum, you won't miss it, your taxes will be reduced and if your company is matching then more free money. If you change jobs then you can align this money into a self directed account.
BP is a great place to vet out your ideas, keep looking for your best options.
Lisa