1998 Vauxhall Corsa Sensors and much more!

Electrical problem
1998 Vauxhall Corsa Two Wheel Drive Manual 84000 miles

I have a few problems with my car.

I have a broken heater flap under my dash board- how much would that cost me?
I have a broken hand brake - how much am I looking to get that fixed?
Can I fox these myself?
I have been told I have a mass oil leak to and the garage wanted to replace the parts including my clutch as they said it was near there and if it got oil on it, it wont work! They said if the work is not done all my oil will leak out in a few weeks and ill have none left! I told them to leave the work and I would look at it myself! This was in may
My oil has never changed I have checked when the engine is cold and when its warmed up several times!

The major problem with my car is - when you start it up and try to drive off pretty much straight away its as though the car is being starved and then it like having kangaroo juice in it! Once the heating has warmed up its not too bad however if you take it over 40/50mph its as though something has stopped feeding it. And the engine management light flickers on and off! If I pull over and restart the car its fine for a while then does it again.
I have had a diagnostics test done on my car and it says it is the o2 sensor, I have been told I need to replace either the Lambar sensor or the MAF sensor, can you find out which one it is as I dont want to fix something that isnt broken.
This has been happening for a while now and has got progressivley worse. It started after my mum took my car to a new machanic who was supposed to fix my handbrake cable for it MOT. (The cable is broken its been sheared in 2!) This machanic Jet washed or Steamed Cleaned my engine, whilst my mum was on the phone to me. I told her to tell him it would brake my sensors by doing this. He said it wouldn't!
I have tried engine cleaner and fuel cleaner. I have cleaned the air filter.
Untill this year my car has had a full service before its MOT, Its had a new oil filter, air filter, spark plugs, clean oil and everything this year however it hasn't. Its had a full exhaust only 2 years ago and a new crankshaft sensor. I am also told that my exhuast is blowing again near the front or the car.
When I first bought the car it had been steam cleaned and needed a sensor replacing not long after, vauxhall told me that steam cleaning had caused this and not to go near the engine to clean it with anything other than a gental sponge or paint brush or just not bother cleaning it!

Last question - can you prove whether having your engine jet washed or Steam cleaned has caused the sensors to brake? : ] This is to determine whether mother bear pays for repairs or me! : ]