Under promise and over deliver

I see a lot of hopeful adoptive parents that are unsure of how to navigate the beginnings if an open adoption. Its hard to tell how much openness will work for you before you actually have the baby. But it's only fair to let the expectant mom know what to expect before she places with you. My rule of thumb is to under promise and over deliver- promise the very bare minimum of what you can do. If you can do more visits or uodates, that's excellent! But you are likely to hurt your relationship with the expectant mom if you promise more than you can deliver, rather than the other way around. Has this concept worked for you? What is your "bare minimum?"