Nobody can comment on specifics without knowing the measurements of your current setup. What can be confirmed is that YES, with a replacement install (sits inside the sheetrock returns) the new window will sit further inward and therefore push your blinds in. An install with nail fin will NOT sit as far inward, but could still sit farther in than your current window IF those have a more narrow jamb depth than 3 1/4". On the plus side, the fact that your contractor is talking to you about this is very encouraging, many don't. He should be able to answer your questions in greater detail.

3/4" is in the normal range. You can usually still mount them to the head jamb by pre-drilling some new holes and getting them in there. They will usually stick a bit proud, but nothing much.

If you use a nail flange, how far does the new window normall come in ?

i know a normal replacement is 3 1/4.

A new construction window application will not usually change the realized jamb depth.

Windows on Washington, if a regular replacement with drywall return comes in 3/4” more, using a nail flange means it will come in 3/4” less than a standard replacement sheetrock to sheetock?

It depends what the jamb depth of the existing window is as well as the measurement from backside of nail fin to inside face of frame. It could end up sitting in the exact same spot, or it could off. We can't tell without that info.