MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
My calculation was such, that if for 200x200mm headbed 144-166W is required to reach 110°C. Than for 100x100mm roughly 36-42W and for 125x125mm up to 64W should be just fine for possible future PCB heatbed, that is not designed yet.
Hotend is quite sure. It have consumption c. 40W at 12V when preheating (If you will use 6R8 resistor instead then at 12V 22W is be just fine) and just 9-16W when hot end is preheated and machine is printing.
As I would recommend 40mm fans to cool down the X, Y, E motor and hotend, 4W more should be good idea.
The motors have consumption 1.2-1.8W each and I think Arduino is runnig from USB power supply.
So 44W (or 40W PSU with voltage set to 11.5V) is just fine to preheat the hotend while fans are running. If you are impatient and want to move the motors while preheating, 10W more is good idea. Means total 54W in worst case scenario for the machine as it is now. It will consume only c. 30W when printing, so there is really no reason to look for bigger PSU.
And if anybody ever will make PCB heatbed (I'm pushing my friend, but need him for some other project right now), than the up most limit for printer with 100x100mm heatbed is somewhere around 96W and 125x125mm heatbed 120W at 12V. But If you will always preheat hotend first, than the PCB, and then start the print, you can go as low as 70W respectively 95W.
So make up your mind, what is the best set up for you.