Re: sRGB or RGB ?
Ok, let's take this from the top.
Screen calibration. A computer screen will, over time, display an erroneous colour and should be re-calibrated periodically.
This calibration will be set for the default for that screen.
This handy programme will allow you to calibrate the screen so you are not showing colours with a blue/red/green hue to it.
This only has a bearing on the sRGB and RGB in photo editing in that with a poorly calibrated screen you will produce images that have different colour hues to them, as your base colour scheme on your computer is incorrect.
sRGB has the same colour range as RGB, only the colour is muted. The photo editing package's default is to sRGB so I would go with that - I do. If your package is defaulted to RGB, go with the flow.
I may change the colour for a particular photograph to RGB if I want a more vibrant colour.
I hope this helps.