Answers (related to my experience as an Astronomer/Astrophysicist);
(1) Not very competitive at all, as a “normal” Astronomer/Astrophysicist.
However, it is VERY competitive in the military/private corporations.
You DO have to safeguard your ideas/theories though. Don’t doubt that the corporations/military will “put you over a barrel”, if you come up with something revolutionary. They will.
(2) Watching a Total Solar Eclipse in 1977. I fell in love with the “daytime stars”. Satellite tracking and UFO sightings, just quenched my thirst for knowledge and understanding more… That’s what got me into Astronomy.
What got me into Astrophysics (and high-energy particle physics) was mucking around with my mate’s Backyard “Underground” Particle Accelerator (which he somehow built from scratch – a bloody genius).
(3) I do my astrophysics in the day (theory), astronomy/satellite tracking at night.
Each day spent in the field is wonderful.
(4) The field is mostly theoretical (astrophysics). Astronomy is much more hands on – especially if you have access to a good telescope.
For career information 9in America), try sites like this;
http://www.jinaweb.org/html/jobs.html
For job vacancies – “New Scientist” magazine sometimes has some good positions offered. Also,
Please note, however, that this is just my personal experience. It is unusual in some respects, as I am “not employed by any official agency”. I am (now) a renegade Astronomer/Astrophysicist…
Maybe somebody else can post their experiences.