If you get the RCD and/or SCM i would highly recommend getting their respective breakout modules. it promotes the jumpers on the back of the module to front panel toggle switches.
i'm not 100% sure what you mean by an "on button" but there are a variety of power solutions available, and whether you need rack space for power is completely dependent on which one you use. i use the 4ms row power which is a 4hp module that uses a laptop power supply. it can also be daisy chained if you have more than one of them.