Commercial rating?

So I've got my instrument rating, complex endorsement and 450 hours PIC.
So I've starting thinking about the commercial rating. But I've got some
questions:

- I understand there isn't much airwork involved and that it's mostly
about knowing aircraft systems. Is that correct?
- The requirements state I have to have made a 300nm solo flight. Does a
flight with a non-pilot count, or do I really have to have been alone?
- What can I do with it? Can I offer to fly people somewhere for money?
If I want to take pictures from the air to sell, do I need a commercial
rating?
- How different is the second class medical from the third?
- If I add on a seaplane rating later, will it automatically be commercial
or is there a separate checkride for seaplane commercial?
- Is adding a commercial rating one of the things that non-citizens need
Homeland Security/TSA approval for?

--
Paul Tomblin http://xcski.com/blogs/pt/
Reliability went through the floor, tunnelled its way to the centre of
the Earth, and perished in the magma.
-- Saundo