If you have a large enough card then it is perfectly alright to just shoot away with it on P and then edit back on the computer. Yyou could even go as far as to do exposure bracketing (look it up in your manual if you dont know how to do it on your cam) so you have 3 slightly different exposures of basically the same shot - i found that a very effective way of doing studio product shots when i worked for a shop which sold stuff on ebay - tis quicker to do the choosing of the shot on the computer afterwards, than fiddle around with settings on the cam.  Also i would look into/play around with the different type of light metering the camera offers so you know what to use in certain situations. 
Those two things will help to get you a better pic out of the P setting, depending on your quality expectations you could also look into shooting raw - but raw shooting with exposure bracketing means you need a LOT of memory.
Personally i prefer Av - just change the aperture - the sweet-spot for most lenses in terms of sharpness is around f/8 so just put it to f/8 and let the camera work out the exposure - similar to P but you have more control of both keeping the aperture nearer the sweet spot - or if you have a really decent low aperture (and by that i mean a crisp f/3 and below) lens, having a lot of control over the DoF. Which is something i know product shots take advantage of ;)

Cant help with the second point tho sorry - never done it myself.

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

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