Cutting out OR over-revving + grating brakes

Hi,

I've got a series of problems with my Citroen Xsara Picasso that I think are probably related because they all started around the same time and seem to be getting worse together! The mechanic I use (who used to have Picasso himself) has never heard of the issues I have and the things he has so far tried haven't fixed it. Wondered if someone here might have had or heard of the same thing and can give me some suggestions to take back to the mechanic?

The car is a 2005 Citroen Xsara Picasso 1587cc petrol engine.

First issue: Stalling
When starting the car in the morning or after it has been stood idle for a while it is needing me to press the accelerator as soon as I turn the key or it dies on me. If I've been driving a while then have to stop and start again it doesn't usually die but it is more prone to stalling in general.
Once I've got the car moving, as soon as I have to slow right down or stop at the first junction the engine usually dies on me & needs restarting. I'm not sure if this is something to do with pressing the brake pedal. Sometimes it will do this at the first 2 or 3 junctions before it stops doing it.

Even when the really bad stalling is over, clutch control at low speed is like walking on eggshells - I'm regularly having to start the car again 2 or 3 times when reversing into a space in the work car park!

Second issue: Automatically over-revving
This is like the reverse of the above and it only happens if I've been driving for an hour or more, say on a motorway, then come back onto regular roads with traffic lights or other reasons to stop for periods of time. While I'm sat there at the lights with the car idling, the engine starts revving loudly like I'm pressing the gas pedal, without me touching it. A couple of times I instinctively tried pressing the gas pedal in a desperate attempt to try clear it, which was a mistake because it then stays at the even higher revs even when the foot is off the pedal, until the lights change and I move off. Movement seems to bring it back to its senses.

Third issue: Brakes that sound like 2 rough metal plates grinding on each other
Even lightly pressing the brake produces a loud grating noise that makes pedestrians turn round and look at the car!

So, do all these point to a specific problem?

There are no fault codes or warning lights.
The mechanic has suggested we pick up a second-hand but working manifold and see if swapping that out helps. He did suggest at one point a new temperature sensor but seems to have concluded that can't be the cause now. I searched the web but didn't find anyone detailing the combination of issues above, just single ones. Some mentioned a switch on the brake pedal being a possible issue. I mentioned that to the mechanic and he said it won't be that.

Thanks in advance for any help.