As the below picture shows, I included the footprint of all the parts that will be attached to the front and back panels which necessitated the slight size increase.
On to the transformer itself. Turns out that a custom-made transformer will cost $112.32 and will take 4 weeks to be made and longer to ship to me which is a big fat no. This caused me to chose to use this R-core transformer from ebay instead.
The 110V/220V input will still allow me to offer mostly international voltage selection. The upper voltage from the output assuming a 240V input will be 17.45V which the DiYinHK regulators can still handle with a breeze as the maximum input is 20V. Also, I have a bill of materials from mouser but my credit card is unfortunately disabled so I have to wait until it's re-enabled before I can restart the process. If anyone is curious, here is the BoM I've racked up so far for this DAC:
Keep in mind that this total does not include shipping prices, will increase due to the cost of the case and decrease if more parts are bought in bulk.
As for the switches, I ended up reverting back to the ONPOW switches for now as they are the only ones which make switches large enough for my spec. Here are five out of 6 of the options for colours available (taken from here). Personally, I like the white and blue!