Assuming you have insulfrog turnouts, you don't need to insulate them. It is already built into the turnout. Electrofrog turnouts do need to be insulated with gaps in the rails leading from the frog. A crossover, of course, would need two gaps, one for each frog. If you are unsure about which kind of turnout you have, test them with a multimeter. An insulfrog switch is dead in the frog and will be indicated so in a continuity test. The electrofrog will be powered by the switch point touching the stock rail. Again, a continuity test will show that.
A bus is pretty simple. Just run two lines of heavy gauge wire under the layout - one line for each rail, roughly following the route of your main line. The power output lines of your Power Cab go to the bus lines. Then drop feeders, generally lighter gauge wires, from the rails to the bus lines. Make certain your feeders from one rail all go to the same bus line because crossing them will cause a short. Add feeders for each branch line and for each yard track. I like to solder my feeder wires to the rail joiners before laying track. It's a neat way of hiding the wires and saves plastic ties from melting under the soldering iron. The drawback of that method is that it is possible to have a loose rail connection in the joiner and therefore a poor electrical connection. But with a little care, it works very well.
Tim
As long as you use DCC friendly turnouts no insulation or gaps are required. These would include Atlas, the newer Walthers/Shinohara and (I believe) Peco turnouts. If, however, you use older non DCC friendly ones, opposing turnouts (i.e. those at either end of a passing siding) will need to be gapped just beyond the frog towards the opposing turnout. Gap both rails leading to the frog. Be sure to fill the gap with a small piece of styrene or the rails may slip back and cause a short. (Don't ask me how I know.)
Good luck!
TJ
Another thought just hit me. If you have a reverse loop or wye, it must be isolated from the rest of the layout with gaps in both rails. A simple solution is to wire it from the bus through a DPDT toggle switch so you can manually control the polarity of the rails. Set the toggle so the train can enter the reverse without shorting, then while the train is in the reverse loop throw the toggle so it can exit the other end. Easier is an auto reverser which senses your train entering or leaving a reverse loop and automatically matches polarity for you. Tony's offers one for $44.95.
PS: I run NCE too
Here's a web site that should answer all of your questions.
http://www.wiringfordcc.com/
Craig North Carolina