It is a good idea, in this green and pleasant (wet!) land, to keep the accessory wiring and track wiring separate.
That way, when a Cheshire killer-squirrel nibbles your feed to lights in the station, shorting out the wires, you can isolate the accessories, and still play trains.
Personally, I would run a separate 12V - ish feed around for lights, water-wheel, that sort of thing.
You can use accessory decoders, to switch these things on and off, but I would keep things simple to start with..
The 'tube' you run the wires in, could be an old length of garden-hose? But in my experience, this is way too small for once your garden empire expands.
Think of it like a real township:
They need power, street lights, telephones / Internet (that bit is your control-system).
If you start adding control for points, you will need 'buildings' to house accessory decoders, wiring out to the point-motors.
Wiring to detect the train, as it approaches the level-crossing. Flashy lights at the crossing. - Possibly even barriers.. Wires, wires and more wires..
PhilP.