Wire in parallel, all center studs (pukos) fed by the red circuit and the rails fed by the brown. Recommended feeding is every 1-2 meters to assure good current availability. DO NOT hook up the track (either feed) directly to the transformer!

As to screwing the track down, may of the folks on this forum don't. Some use two sided tape to keep the track from moving. I screw them down. If you are using K-track, on each section there are two or three small indentations in the ties or sleepers. Put the screws through there (it takes some force to penetrate the plastic). That is the only place you can screw them down without drilling through the metal substrate of the track. I paint the screw tops with flat black after installation to hide the screws.

If you are using C-track, there are small indentations int he plastic between the ties for the screws to go through. You have to penetrate the plastic.

What many do is run a "buss" set of wires under the layout and tap off of that. That is the cleanest way. Recommended wire size is 16 AWG (1.0mm2) or larger. Otherwise you can use distribution strips such as the Brawa 2591 or 2592 or the Marklin 72090. Note that the Marklin one is for the new Marklin plugs and will not be interchangeable with the old style plugs as used in the Brawa strips. As to the screws, Marklin sells special screws for K track part number 7599 for a box of 200.

Here is how I wire the k-track http://layout.mixmox.com/1/laying-track
And you can see how I run the bus lines here http://layout.mixmox.com...lsectionframingandwiring
Wire gauge and how I tap into the bus at http://layout.mixmox.com/1/20020224Wiretaps
and http://layout.mixmox.com...ringandpigtailconnectors