I find that 50mm is neither here nor there for me. A cheap and good lens, however, it seems to be best for more predictable situations, ie, taking pictures of a friend, or from a fixed spot, like concerts.
Little India, it depends on what you're taking. You mentioned people, how far do you plan to be from them? for 50mm, 10 meters is too far, 3 meters is a better range, but you get attention of that person, some may not like it and you may not feel good about it. If you're going to be outdoors, I recommend a zoom lens, something like a 55-200? I'm not sure what have you on Sony. Indoors, get either a 85mm or some F2.8 wide angles? (may be expensive!)
A 50mm on a 35mm format approximates what the human eye covers, and is a pretty nifty lens to use because of this *natural* field that one can cover with photos.
I do not think there is an obsessive need to strictly have a 50mm approximation for use. BTW our eyes actually covers a slightly larger area ( and infact some refer to 43 mm as a better approximation ).
Correct. Any lens stating something like f/1.4 or f/2.8 has a constant aperture over the whole zoom range. Prime lens don't have a zoom range, naturally. If you look at many zoom lenses you'll notice something like f/3.5 - 5.6 or f/4.5 - 6.3. That means that the biggest possible aperture is not constant but varies depending on the zoom setting (focal length). The biggest aperture (e.g. f/3.5) is only valid for the smallest focal length (e.g. 18mm). If you change the focal length (zooming in) the maximum aperture goes down. Further details you can find in the lens reviews and lens data of the manufacturer.