I am a transracial adoptive mum and had to have some training about these issues. We all want to believe that being part of our family is enough, however read any account of adult transracial adoptees and they all say that it worked against them if their families did not acknowledge their heritage. It's very likely that your child will want to explore that half of him at some point - although it may not come until adulthood.
I share the reservations about uploading potentially sensitive data to the DNA databases, however plenty of people do it. You may find gold, it may just open up a whole can of worms eg other birth family members with whom you were not ready for contact with . Identifying ethnicity is only as accurate as the number of people of that ethnic group already in the database (as far as I understand). I know people who have done it for their child and got answers like "half Caribbean" which is obviously still very vague but at least they have an idea.
If your child does not resemble you then the world is full of the "is he yours brigade?" and no matter how rude it is, we have to learn to deal with them because we can't stop them. This will also go for your child at school. So might as well talk about it when he is old enough and prepare him for any questions.
The learning from interracial adoptions has been overwhelmingly in favour of honesty and just keeping talking about it. I can't tell you whether to do a DNA test or not (I am curious to do one too but have reservations). Some parents wait until the children are old enough to agree (although then you have to manage their feelings regarding the results).
Like everything in adoption, there is no easy answer. However ignoring any side of his heritage that you don't share won't be the answer.
These are just my thoughts, I hope it helps.
Good luck!