Erick,
This is nice first try, you are on your way for much better job and it is definitely worth continuing :-)
As far as ASA setting is concerned, I found it best to stay at highest value (Canon), but it is not a rule, and in some cases the dynamic range may be compromised (depending on camera model).
There was a thread on IIS, discussing this.. someone showed (by means of mathematical analysis) that the best S/N is at high ISO, which, for me, was not surprise.
When I find it, I will post a link.
Avandonk (Bert) knows a lot about this subject (middle of the page):
http://www.iceinspace.com.au/forum/s...ight=S%2FN+ISO