Download 'Step motor basics.pdf' at www.geckodrive.com/support.cfm That white paper explains most of what you'll need to know to get started using stepper motors.
I know that you've written that you're not using Gecko stepper drivers, but I've used this general forumla to size power supplies for several years:
AMPS = SUM(amps required for all motors) X 0.66
Voltage = Minimum, 10X motor's rated voltage, Maximum, 20X motor's rated voltage
In your case: 1A + 1.2A + 1.2A = 3.4A and 3.4A X 0.66 = 2.24A, 5.2V X 10 = 50.2 V, 2.6V X 20 = 52V. So, a power supply that produces at least 2.25A at 50VDC would be my starting point.
If I were building my own power supply, I could buy a toroidal transformer (AVEL Y236654, $46.10 from www.partsExpress.com), a 10A 100V bridge rectifier (less than $10), and a computer grade 63V 15,000 uF can-style capacitor (about $35). Or, I would buy a complete unit from AnTek, such at the PS-3N50 for $85 (www.toroid-transformer.com).