From the site:
Why a Foundation?
First and foremost, the reason to start a foundation is to fulfill a philanthropic mission.
Many foundations are set up with the notion that the endowment is to
be permanent. Even small endowments, by providing persistent funding to
a cause or charitable organization, can create tremendous public
benefit over years.
Is there a minimum recommended size?
For a simple, permanently-endowed foundation, many advisors think
$500,000 seems to be a practical minimum. This estimate seems to be
based on the assumption that the foundation will hire professionals,
and if so, little income will be left over for grantmaking. However,
this assumption is simplistic and does not reflect reality.
More good stuff on that page. They also provide useful links: