I'm going to go out on a limb here and say that if you have to ask such questions, chances are you shouldn't be trying to turbo your car. Doesn't sound like you have the slightest clue what you are doing.
But to try and answer those questions...
A 325e wont like alot of boost, and there is no point doing just a little boost.
Tap the oil pan for oil inlet.
Oil pressure switch is located under the drivers side motor mount.
I know of 325i's (m20b25) producing 250-300hp. I know of m20b28 strokers makeing 300-450.
No one turbo's an eta, if for no other reason then its revlimiter. If your turbo starts to spool at 3,000RPM you hit the revlimiter 1500RPM's later. Pointless.
It would be best to build a proper engine to accept lots of boost, then halfass boost an eta.