Quite possible to do all that.
I've got a small 3D Printer - it'll do about a 130 mm cube - so I'd have to do the manifold in sections to be glued together later into one complete unit. There's larger printers (such as the Makerbot 2x) that'd work a bit better though.
Mine's a layer deposition machine so the finished part leaves thin ridges on the surface (about 0.2 mm thick) but they can be easily sanded off and also rubbed with a cloth soaked in acetone.
I believe it's also possible to use the ABS plastic they use to make a sand-cast mould, as the ABS burns away with no residue when the metal is poured in.
Anyway things like this are pretty easy to make ...http://www.thingiverse.com/thing:25207
For the larger parts you slice them up in software, print them out, then glue them together.