Planning an addition - any plumbing device?

I have a two-story 1500 sq ft. house in Albany, NY, with coper pipes and a 50 gallon gas water heater. Most of the existing drains cast iron and are 2" feeding into 4" drains that run down into the basement.

I'm planning an addition and am working with a licensed architect. He's promised me 'building permit'-ready plans, that don't include HVAC, electrical, or plumbing details. He's told me that the general contractor that will do the job will have his subcontractors for those services provide the details for those plans.

On the second floor of the addition, I'm planning a new master bathroom that will have a separated shower & tub, a single toilet, and two sinks. How close do the shower/tub/toilet have to be to use the same pipe/vent?

On the first floor of the addition will be a new kitchen with a sink, dishwater, and island where I plan to install a small sink (planning on using an AAV there).

Also on the first floor will be a new laundry room with two washers, but no laundry sink. The washers should be directly under the two master bathroom sinks. I thought they could share the same drain line.

And, just to complicate things, I've got to use water conservant fixtures that use 30% of the standard flow rate because I live in an area where the sewer and storm drains are combined...

I'd like to get some advice from some experienced plumbing guys on things that I should consider NOW, before the building plans are drawn up. Thicker walls, wet walls, etc.

Are there things that you've seen architects forget in plans that I should remind him about?

Any advice would be appreciated.

Thanks,
Todd