Hello Mel and welcome to the forum
I'll try and answer to the best of my ability, which is limited
1) Could be either; FUBAR motor or chaffed wires in the door shut. I'd check the wires first and go from there.
2) Knocking sound could be one of a few things, not my speciality I'm afraid. No doubt it'll be something to do with the suspension though. If you are able to either get under the car yourself or get a mate, you could do a visual inspection and give each part of the suspension a good tug......if anything moves too freely, it'll probably be that part at fault - that's as far as my knowledge goes I'm afraid
3) You can put a replacement CD player in but you will need a fitting kit. Something like this
one. You may also need an ISO adaptor if you have steering wheel controls that you wish to continue using.
4) You'll have two manifolds on the car. The inlet manifold
which will either be on top of the engine or on the front which is the last part of the air intake system before the air enters the engine and the exhaust manifold
which is the first part of the exhaust system. Normally, if either of these are 'blowing' it'll be a warn gasket.
5) If you go onto My Renault
you may be able to download a manual in PDF format. If one isn't available, contact Renault thru. the site and they may be able to post you the manual on disc
Phew....hope that's helped somewhat