Is there any real benefit to getting a faster rpm? Can the difference be detected?
Yes it can. You'll notice a difference in load times on applications, boot, basically anytime your laptop has to go to the hard drive to gather data it'll be faster. Personal opinion thou.. Look or wait for a nice ssd to be on sale/bargain. You'll notice the biggest difference with an ssd. Worth every penny.
Yes, 2.5" sata is what you need. Other specs do not matter.
If a SSD has the capacity to hold your data, then do what you must to to get one.
It will absolutely transform the performance of your pc, regardless of the power of the cpu.
A SSD is 50x faster than a hard drive in random access which is what we do mostly. It is also 2x faster in sequential than any hard drive.