Postgres Licensing

May be this is the wrong place to ask the question. Still, answer me if
someone can or please redirect me to some place where it can be answered. My
questions are:

1. PostgreSQL can be distributed freely according to the license terms. Can
it be sold (for a price) without changing anything in the source?

2. Does the license restrict me from adding my closed source additions to
the project and then sell the product? I want to add in a few files here and
there which would be closed source in nature, while all the changes made to
the original files will be open, and then sell the modified database with a
dual license. Is this possible?

May be you guys are hard core OSS enthusiasts and may flame me. I request
not to and please consider my question.

Thanks a lot.