W203 '03 C270CDI - water pump removal directions needed

Greetings - for the past few days, my 107,000 mi 03 C270cdi ( South African assembled) has been emitting alarming puffs of water vapour from under the hood at standstill, when fully
warmed up after either highway or city driving. It is also losing coolant very slowly, and not pressurising the cooling system much. My main suspect is the water pump - all hoses seem ok, no symptoms of head gasket failure, radiator is dry, some wetness around the front of the engine bay that looks like it has been flung around by the pump pulley. It may have been failing slowly for some time - maybe twice in the past 35,000 miles the warning for low coolant has come on, a small top- up has dealt with it each time. I think the puffs of vapour are caused by drops of coolant landing on hot things when the car is moving - the puffs stop after a few minutes ticking over. Temp gauge goes no higher than 85 degrees. There is a squeally sound from the front of the engine on tick-over which I think might be the pump bearings giving up.
My request for help and advice from the group is:
(a) does my diagnosis seem reasonable - are these pumps known to fail at this age/milage?
(b) what is the right way to get at the pump, how much of the radiator assembly will have to come out? There seems to be an awful lot of plumbing to be disturbed if the radiator has to come out to gain access. There is not much free space around my engine - 5-cylinder.
(c) How much coolant does the system hold - just so I buy enough with the pump from the MB dealer.
Regards, & thanks in advance
John
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