You can get an electronic boost controller that has different max boost levels for different rpm. What options exactly are available depends on the boost controller. I see no reason to have the boost controller keep the boost at 0 psi until 3000 rpm, that'll just make the turbo take too long to spool up. But yes, you can make a boost "curve" with different boost levels at different rpm.

The stock ECU isn't capable of reading a signal from the MAP sensor which indicates boost. There are a few ways of tuning the fuel, which one you use depends on a few factors. I would explain how exactly the Honda fuel injection system works but I've done it so many times before. Do a search for "duty cycle" and you should find a few posts on it.