About the glass - please post some pictures and show us what looks wrong. Generally, glass should render just fine and very quick using a basic glass material (diffuse=0 or 100%black, refraction level=~1, some reflectivity). Maybe you are getting noisy caustics? This is a bit problematic for Corona at the current stage of development. Caustics may refine quite slowly.
About the gi/aa balance. This is really simple once you get it. :) Basically it looks like this:
For default settings (gi/aa=16, LSM=2).
each pass = 16 samples per pixel for indirect light, 32 samples per pixel for direct light, and 1 AA sample.
After 16 passes you get 16AA samples per pixel. They make object edges and textures look nice.
By indirect light we mainly mean light bounces.
By direct light we mean light cast by lights, sky, sun, etc.
More GI samples will give you better GI solution (like noisy areas in corners) also better glossy surfaces.
More LSM will give you less noise in direct light.
More passes will give you better edges and textures.
Increasing GI samples or LSM is always at the cost of time needed to finish X passes (or at the cost of number of passes in the same time).
There is no "universal" settings for every scenario, usually you need to experiment what settings will give you slightly better performance.
And last one, but possibly most important: default settings work quite well in most situations. :)
