lowered floor OK
here are some things I feel comfortable commenting on.
1. You maybe don't have to build the floor up. As shown below. The shower p-trap might not get in the way. The toilet (which has a p trap inside it) needs room for its drain. Another thread i commented on in the Toilet forum had the same problem of needing to sit an inch high so the drain would connnect.
2. The top part of the vent can be built as shown below. No need to run separate pipes.
3. The washer drain connects into the vent pipe first, before connecting to the drain.
How you get the vent through your building 'envelope' (i.e. to the outside) is not something i can comment on.
I am not a plumber. In my municipality, and in my high-rise concrete building, I wouldn't need as much venting as you have shown - with four vents for four drains/fixtures. I am not a plumber.
david