If I recall correctly, the US allows individuals an exemption of something like $75k in foreign income that you don't have to pay US taxes on. I don't know if the number has gone up since I lived abroad, and I also don't know whether it applies to a business. I guess if you are a sole proprietor, it does, but don't take my word for it. Check with the IRS or an accountant.
This may be an odd question, I don't know...but if you called the US consulate, might they be able to point you toward some resources? They might even have someone on the consulate staff who knows the answer. (This just seems like the kind of thing Americans living/travelling abroad might have on a semi-regular basis. Not as regular, perhaps, as "when do I have to renew my visa", but they might know.)