There are curently several websites online which offer 'power supply calculators' and they also do provide an info table for quite a number of brands of PSUs. If you are asking for a software meter/real time gauge, not of any that I have known of. In general, 500w-650w gold efficiency power supply is the norm and definitely capable of handling most, if not all single gpu systems. If you have not experienced the random shut downs I talked about previously, most probably your PSU is fine. Personally for me, I would go for brands like seasonic, corsair etc for their PSUs. There are a couple of new threads here with regards to PSUs, do check them out.
As for your 2nd question, the components that will consume high power in general are the cpu, gpu and sometimes the mobo and sata blueray/dvd drive. Contrary to your belief, hard drives and ram are very low power consumers! If you want to even lower the power consumption of your hard drives, go for ssds/2.5" type of hd instead of those 3.5" type. The reason most cases today provide plenty of drive bays is because some people prefer to do raiding of multiple drives for performance improvement, especially when they need to handle read write data of humongous sizes. Even when one is not raiding, aesthetically it is also neater to house multiple internal hard disks than to have multiple external hard disks lying around together with those usb cables haha (not to mention about the hassle to 'plug & play'). Having more internal hard disks will also mean that you have freed up more usb ports. I do believe that quite a number of these extra drive bays are removable- if you do not need them/need to install a very long gpu card.
Cheers.