Rotating squeaking sound, drop in rpm when pressing accelerator

[swemegII]

I recently bought a Megane 2004 1.6 16V (K4M) with approx 60000km on it to use as a daily commute/beater car.
Initially the car had some minor issues but most of them got sorted out except for three things.

1. If I leave my car over night and try to start the car, the car cranks fine and starts up with idle at approx 900-1000 rpm. As soon as I hit the gas pedal the rpm drops significantly and almost stalls (for a second) but after that the car works fine.

2. When driving down the road, I can hear some kind of whining sound at higher rpms. (2500-3000 rpm) It only appears when I'm at higher revs and pressing on the gas pedal, otherwise the whining is not present.

3. When the car has been driven for over 30 mins and the engine is at working temperature, some sort of rotating squeaking sound appears and I'm having troubles localizing the sound. The sound disappears as soon as I disconnect the breather pipe from the air pipe connecting the intake manifold with the air filter. If I turn off the car and start it up again, the sound starts after 2-3 seconds.

YouTube video of the squeaking:
https://www.youtube.com/watch?v=OjFf7tLlmak

Any ideas what could be cause(s) for these issues?

I somehow believe that they are all connected as I've done the following:

1. Replaced the alternator (brand new)
2. Replaced gaskets on the inlet manifold
3. Replaced throttle body (brand new) + gasket between intake manifold and the inlet.
4. Replaced the air filter
5. Replaced gasket for the crankcase breather pipe
6. Checked the coils, none of them seems to be broken, although one of them had some sort of yellow coloured paste on it and the spark plug seemed to be slightly darker than the rest.
7. Replaced the spark plugs to new Bosch ones.
8. Cleaned the TDC sensor (having the old black sensor though).
Worth to mention regarding the TDC sensor is that it refused to start sometimes before I cleaned the sensor, after that the engine starts just fine.
9. Replaced camshaft sensor (brand new)
10. Replaced MAP-sensor (brand new)
11. Checked the voltage of the battery, seems fine and the alternator is charging it as it should.
12. Replaced timing belt, the pulleys for the timing belt and the water pump due to 60000km service
13. Replaced aux. belt and the pulleys

Things I haven't done (yet) but consider doing:

1. Replace temp. sensor
2. Replace fuel filter
3. Replace VVT solenoid
4. Replace dephaser pulley

Any help would be appreciated

[swemegII]

So I picked up this project again and the things that were done was:

1. Replaced temp. sensor
2. Replaced VVT solenoid
3. Replaced dephaser pulley
4. Checked for leaks inspecting rubber hoses and using motor starter spray
5. Cleaned break switch connection

The dephaser seems to have done the trick with the lack of power and high gas milage, although the squeak is still there making me think it's the bearing of the AC compressor or simply a bad AC compressor clutch. New bearing and break switch ordered so will be changing those as well.

If the engine is hot and the squeak was present prior to turning off the car and I start the car back again, there is a 2-3 seconds of idle before the squeak appears making me think it's the AC compressor that engages and starts squeaking.