What's needed for a 3d printer build??

[Neale]

I use Slic3r as well, it's a good piece of code. Also runs on Windows and Ubuntu so I can use it for printing indoors from a laptop and in the garage using my LinuxCNC machine, in conjunction with Pronterface for printer control.
The extruder stepper needs next to no current so should be fine off the ATX psu.
PLA is a good starting point but I would disagree that you need to mess about with PVA, etc, on the bed. I use a heated bed running at about 60C and don't have any problems. However, the top layer of my bed is a glass trivet from a local discount shop which has a ground finish. Getting the "squish" of the first layer on the bed is critical so you need the bed to be level to, maybe, better than 0.05mm so the layer is uniform across the piece. The bed gets cleaned with a quick wipe with acetone between prints to make sure it's grease-free.
Don't need PID for the bed as the temp isn't that critical and there's lots of thermal inertia but PID on the hot end is really useful. I reckon that I need to hold the temp to within 2-3C and without PID that's difficult. Took a little while to tune the PID parameters but I seldom see the temp move by more than a degree or so during a print. I built my favourite hot end with about 24W of heater power so about 2A on 12V. I think the heated bed (about 200x200) takes about 120W off the same 12V supply as the rest.
Just my experience, though - there are as many religious debates in the 3D printing world as, say, the Mach3/LinuxCNC world!