[240racer]

your stock ecu will not have to be replaced to run 7psi.  The Mafs will do just fine with 7psi, it doesn't need to be replaced till you go higher, like 10psi or so.  The only reason that it needs to be replaced is because the air flow is higher then it is designed to measure.  Your stock fuel pump is also fine until 10psi of boost.  However, you fuel injectors are not large enough to support the power you will make with 7psi.  Even if they were open all the time, they would not inject enough fuel.  There are many ways to deal with this.  In general there are two main ways to go about getting more fuel.  One, you can put larger injectors in (370cc/min or larger).  If you do this, then you must let the ecu know about it, or it will always inject more fuel then you need, since it thinks you have smaller injectors.  You can have somebody make a reprogrammed ecu so the ecu knows you have larger injectors and it injects the fuel properly.  These ecu's are generic and not tuned to your car.  They are the safest way to go, but won't always make the most power.  This is the JWT reprogram method.  Otherwise, You can get a piggy-back unit like the S-AFC to fool the stock ecu into thinking that less air is going in then really is, so it injects less fuel (but since you have larger injectors, it evens out)  This is the method I have chosen for my car.  I haven't had a chance to to tune it yet, but so far it works great.  I can control the idle or off-throttle mixture at 8 rpm increments and the full-throttle mixture at those 8 rpms.  So as you can probably tell, you need to know something about tuning engines or bring you car to somebody who knows how to tune engines to go this route (that is why everbody who doesn't know better gets the JWT) There are small variations on the two above methods of using larger fuel injectors (like stand-alone) but those are pretty much your main option.  I have yet to talk to anybody who actually had JWT tune their car for them, instead of sending a generic 240sx turbo ecu in the mail.  I don't want to bash JWT too much, what they do is good and it works, it just might not be the best method of getting the most power out of your setup and money.
The other method of getting more fuel is a rising rate fuel pressure regulator.  This is a unit that controls the fuel pressure relative to boost.  the more boost, the more fuel pressure.  That way you can run the stock injectors to about 7psi.  This is the route nsport has chosen for their kits.  You can tune it similar to the s-afc.  I don't really like this method because of the consistancy.  Also, you probably need a high pressure fuel pump to use this method since fuel pressures might get as high as 80psi.

As far as fuel rails go, if you get DE or SR injectors then you don't need a fuel rail.  if you get generic injectors (from jwt or anybody else) then you need a fuel rail that accomidates them.  You can get injectors to fit your rail from heavythrottle.com

if you are going to go with JWT (not a bad idea if you don't want to mess with stuff) then get everything at once.  fuel pump, injectors, and MAFS. that way you don't have to pay reprogram charges later (one thing I never have to do with the S-AFC)
hope this helps