Very few. The only significant risk I am aware of is the need to avoid certain points in pregnant women. Vigorous pressure could lead to bruising.
Minimal. Acupressure is the use of non-needle pressure to an acupuncture point. This can be done with a blunt object (like a chopstick) or a finger. There is a risk of bruising and possibly breaking the skin (which could lead to infection) if too much pressure is applied. Acupressure or acupuncture at certain points on the body might induce labor in a pregnant woman, but in general the risks are minimal.