I'm not a banker, but here is my basic knowledge of SBA. The interest rate may be different from a conventional loan structure by a little, but there is no difference in the fact that a banking institution is making the loan. The SBA guarantees a portion of the loan to the bank - it does not actually make loans themselves. This is designed to encourage banks to make *risky* small business loans that they otherwise would not at normal interest rates.
Commercial rates almost always track +2% above the home mortgage rate. Right now you can get a low 3.5% home loan so 5% sounds about right. In fact, its a little better than I would have expected.
I think the 10-year option is not a bad option. Here is the deciding factor that would make me pick the 10 year: do you plan to pay off the loan in the 10-year period or refinance to stretch out the payments for a full 20 years? If you plan to pay it off by the end of 10 years, you will obviously save the money. I would stay away from the 3 and 5 year choices. The Fed has been eyeing rate hikes for years now - it will happen sooner or late. I don't have a crystal ball either, but I would be surprised if we're still at the current Fed rate in 5 years.
As a side note to your cost calculations - the banks have the right usually upon calling the note at the end of the period to re-appraise the property and re-assess the loan. And they have the right to turn away the refinancing. That could be a lot of hassle and some extra cost.