The kickback style of plan, where trains travel most of the length of the layout in one direction & then reverse gets a lot of track in, as you've managed here.
The loco depot looks about right to simulate a medium size terminal, maybe try to get a couple more tracks radiating from the turntable?
The first layout I ever got up & running, even though much simpler then this, was along these kickback lines & I was quite happy with it.
I'm no good at electrics but the plan doesn't seem to be hard to wire up.
RIP is a term used in the US, meaning "Repair In Place", essentially for running repairs to rolling stock.
Hope this helps. Good luck.
Shouldn't have a problem with some more track from the turn table. Could probably fit another track either side of the roundhouse if I tried.
Im an ex CETECH from the RAAF, so the electronics shouldnt be an issue I'm hoping 
I was aware what the RIP stood for, I just was not aware it was a US only thing. Do other countries not have that type facility, or is it just called something else ?
The first rule of model railways, is that there are no right or wrong... it is
YOUR model railway (or Railroad if following the USA!)

you can have what you want!
As said, RIP is a US term. I can only comment on SAR as that is what I follow. Should a wagon be found to be U/S (for your RAAFie terminology!

) if in a major yard, it would be cut out of a consist load transferred and depending on the fault, shunted to a near-by siding for fixing, or moved to a works depot for more serious repairs. For example, I'm sure there was a siding in the Mile End Yard for minor repairs, but I do not believe it was ever called a RIP siding. I can find out though.
From the electrics side, as you are starting "new", I
STRONGLY recommend you have a look at Digital Command Control (DCC) over the traditional 12vDC system. DCC offers many advantages over 12vDC.
1) You can have multiple locomotives on the same piece of track going in different directions. Your shunting layout is a good example where you could do this.
2) Trains can be operated more prototypically with headlights, marker lights and sound.
3) Wiring of the layout is "nominally" simpler. Your proposed shelf layout would be verrrry simple! Except for the turntable. It will need a device to swap polarity as the bridge rotates.
4) DCC provides for the future really well and facilitates easier expansion later.
5) Recognising the popularity of DCC, many manufacturers are now offering locos with DCC and sound factory fitted.
There are considerations with DCC,
1) There is an initial outlay for a Command system.
2) Older locos generally need to be retrofitted with decoders, obviously, at extra cost. This is not always simple depending on the forward planning by the manufacturer. Some of the older Austrains locos can be "fun" to retrofit. LOADS of people out there happy to assit with this, including me!
The attached photo is of my DCC shelf layout which is not unlike yours... 1.2m x 0.40m modules for a 3.6m length.
In this image the Power Bus is red/white wires, Turnout motors are blue/black and the yellow is to power the turnout frogs. Gives an idea of the simplicity.
I'll comment on your track plan separately.