The internal header for a TIFF file can be flagged for byte ordering, in either Intel or Motorola format; since nobody in the personal computing world really uses Motorola chips anymore, I'd be willing to bet that Photoshop uses the Intel format (which is what was almost certainly meant by PC in the format description). However, other than peeking into the binary innards of the output file itself, I'm not sure how to verify with certainty that PS is using the Intel byte ordering.

Size-wise, they're wanting your image size to be at least 3600 x 3600 pixels, with a DPI setting of 300.

You might ask them what bit-depth they want, too... there's no point in making a nice (not to mention huge, since it's uncompressed) image in 16 million colors if they're only going to reduce it down.