P3Steel Electronics and wiring
The recommended electronics for the P3Steel is the ubiquitous Arduino Mega 2560 + RAMPS 1.4 combination, used in exactly the same way as in many other Prusa i3 variants, but any controller complying to RIS 1a (since we want heated bed support) will work.
The Arduino Mega 2560 + RAMPS 1.4 + A4988 drivers + 80mm fan as used in the P3Steel make for a neat stack and this combination is very well documented in this wiki:
Another popular combination is an Arduino Mega 2560 + Ramps 1.4 + A4998 drivers + 80mm fan + 12864 graphics LCD controller.
Wiring and Power Supply
To avoid duplicating the excellent information available in this wiki, check:
Prusa i3 Rework electronics and wiring page.
For the power supply, check this wiki page: