Officially there is no minimum spacing between the silkscreen line and any exposed copper. As long as you remember to leave the Silkscreen Clip option turned on (this is default on for every quote form) you can have the silkscreen draw right over the top. Then we will worry about cutting that silkscreen away from the drawing so you receive a clean and solder able service.
If in the event you choose not to have this option turned on then I wouldn't have the silkscreen drawn any further towards your pad than the outer edge of your soldermask opening for said pad. With a draw back of about 5mils. The 5mils added will account for the soldermask registration tolerance.
Customer Support Lead
13626 S. Freeman Road
Mulino, OR 97042
Phone: 800-228-8198 x336