Bathroom addition drain and vent layout advice

[Walt Ritchie]

I am adding a bathroom addition and I need some advice on laying out the drains and vents. The new bathroom will be 8'x 15' and will be slab on grade. When the new septic system was installed a few years ago the septic contractor left me a 4" capped stub-out for connection to the future bathroom addition. please excuse the crude drawing, but this is what I have come up with for the layout and was hoping for a critique and advice on what may need to be adjusted.

Thanks in advance!