Off the top, it looks good to me.
Panels are generally not listed for serving single phase circuits when used with a delta service. Using the panel to feed a separate single phase panel is just one code compliant way .... splitting the feed at the meter, or using a gutter, have their own issues.
Which brings up wire sizing. I can't imagine any way the #3 would draw more than 100 amps.
Side note: Every such service I've seen has actually had only two transformers (open delta). The (much smaller) second transformer also limits the power available to that 208v wire.
