Some questions about 996 Turbo

[Araz1994]

I bought a 996 turbo 2002 model with manual gearbox, and god I love this car! Just amazing! But unfortunately my turbo got broken because of a bad rehault done some years back, that problem is solved and I replaced it with a new turbo from Borg&Werner. I've driven the car around 500km now and notice some stuff.
 

1. I feel there is a pushback/turbo lag call it whatever you want, in the 3,4,5 and 6th gear i feel around 2800 and 3800 rpm the car is holding back some power before the rpm starts moving. Its kinda hard to explain but ill try.

When im pressing the gas pedal around 2800 rpm i feel the car is holding back, i press the gass more, there is a little holdback, and after a second or two it goes like a rocket to 3800prm and sam issue here.

2) I had this issue since day one, some times I hear a whistling sound, sounds like a fan, it's very quiet. When I press the clutch in and release the sound goes away. It happens only sometimes

3) I had this issue too since day one, when I drive in high gear and I can hear a sound sounding like to aluminum/metal plates slightly hitting each other. The best way to describe this sound is like when two aluminum pot collides with each other

4) What should the oil pressure be? Ive read that it should be around 2x the rpm. So if i drive 2000 rpm the cars oil pressure should be around 4 bars, and on cold start it should be 5? Is this correct?

5) I've read several different opinions about what kind of oil should be used, what is recommended and what's the best oil for the car?

6) After the turbo replacement, I feel my fuel consumption is much higher.