Dale says:

From the drawing, the inner loop does not connect to the rest of the layout so you can use one transformer for that. As for the rest, if it were me, I would isolate the inner loop from the rest at three points: the crossover at the top left, the start of the lead track at the front by the track switch, and at the diverging track at the far right and have one transformer for the outer loop and the third for the operational and switching portion of the layout. This would let you use the two loops independently while still doing some car positioning.

Again, if it were me, I would seriously consider using DCC and forget about all the wiring headaches.

Geoff says:

I second Dale’s comments. Put the insulators where he says. And you only need three transformers. As for where you attach, the power leads to the track, it depends a bit on whether the switches you have are “power routing”, ie send power along the track they are switched to, and isolate the track they are switched against. If they don’t isolate, then it doesn’t matter where you connect the three transformers. If the switches do isolate, then you need to be careful where to connect. I’ve marked in blue where Dale suggests the insulators should go, and I’ve marked in red where I would connect the power.