Using your colours to separate areas, I think you need one more coloured zone. The cross-over in the blue to the front, under the two green lines (road bridge?) needs separating, so the line at the front labelled "shunting" is a new colour (call it "red" from here on).
Then, the joint between each coloured zone should be insulated joiners (both rails). Power feed to orange should be below the "S" of "Shuttle" and to blue above the "u" of "Shunting". Green powerfeed along the straight to buffer. And the new "red" area power feed would be on the straight to the buffer at the far right of layout.
In terms of isolating locos, the turnouts would power-switch sidings of the same colour, but you might want to add further insulated joiners (in one rail) and separate switched power feeds to the single rail in parts of sidings to allow more loco storage.