Firstly
Nice looking Europa you have there.
Does your throttle cable have a solderless nipple at either of it's ends? If so it's worth checking that the cable is adjusted correctly as if it is set slightly too tight it will give what you are describing in that the throttle can appear stuck/high idle speed when the pedal is released slowly but a blip can reset it back to where it should be. - solderless nipple will have a small screw that allows you to reposition the nipple along the inner cable. Otherwise it's as Alex has described with the additional possibilities of it being routed incorrectly or maybe it's is trapped/pinched by something?
Handbrake cable is adjustable but you have to access it inside the centre tunnel via the access hole - bit fiddly tbh - 'U' shaped piece on the rear cable with central cable from this to the translator (the pivoting bracket you have found under the big bung in the front plenum!). The central cable has a threaded end that passes through the U shaped part and this is where you adjust it.
Might be worth checking the condition of the rear shoes and their operation too as they may be binding slightly rather than it being the handbrake cable adjustment?
Banks is one of the best sources for any parts you might need in the U.K. If you get the opportunity to speak to Richard on the phone then he is also a very good source of information/advice.
Regardless of how your fan is controlled it is also worth making sure that it is spinning the correct way! - fairly common for them to be connected up incorrectly which doesn't help very much!!
'Gunk' is a pretty effective product for removing oil etc - should be available from most motor factors. Spray/brush it on and wash it off with water.
Jon
