I have one sage word of advice. This is possibly the biggest life saver and game changer for me:
DetailSander. (It's one word if I delete the space!)
I have a black and decker Mouse corded sander. It cost like 35 bucks, but it was worth it. Hand sanding is such a pain, and rough on your wrist elbow and shoulder, I was getting to the point where I had to take a few days off to recover. The mouse pays for itself in how quickly you can smooth down a terrible rough bondo job.
Orbital oscillators are great for broad areas, but a mouse gives the same capability, as well as being able to hit corners, or using the finger attachment to get narrow areas, like the recessed area with the three "teeth" on the back of the ODST helmet. As was mentioned earlier, triangular oscillator, this is just a pointer at the one I use. A lot of them don't come with the attachments, which I think are very important for halo modeling.
The one downside is they have terrible heat management, so if you use it for like an hour straight without giving it a rest, it can start melting the plastic components inside. I read that you can fix them pretty easily, but I am too lazy right now, maybe later I'll repair the old one as a backup:
http://fixwiz.blogspot.com/2008/08/black-decker-mouse-sanderpolisher-ms500.html
I've killed one so far when I tried to use it to refinish my stairs. The second one has been going strong for smoothing out pepakura pieces.
There is a better one out there by Bosch, but it's 120$. If you can take good care of the Mouse it should be a decent all purpose sander.