very unlikely needs a new ECU, this is very rare.
blue smoke can only be oil burning. on turbo derv motors this usually means that the turbo is throwing a bearing and its leaking oil through into the air side and burning it, however it could be over filling if someone has been a bit special with it.
the fault codes really are pretty good when it comes to these sort of things it will tell you almost for definate whats caused the fault.
with the crank sensor you should get the engine management light on and it does have its own specific fault code.
typical symptoms of the crank sensor failing will mean the car cuts out when it gets warm / up to temperature and will refuse to restart until it has cooled down again. then once it warms up it will again cut out.
cam sensor again should have its own fault code although these are somewhat more stable and not as known for failing as the crank sensor so I wouldnt worry about that yet.
I would consider changing garages by the sounds of it, I think these lot maybe giving you the run around somewhat. the italian electronics are a most complex and unusal beast and if you have someone that doesnt understand its unique complexaties then you really could be wasting your money! a specialist is really worth their weight, although avoid the dealer network.
you are doing everything right so far, just keep at it. I've had a similar up hill struggle for about 4 months with a 1.9jtd m-jet I bought but am finally on top of it now. you will get there.
also be aware that if oil has made it through into the air intake side of the turbo even if you cure the leak or cause of leak it may take some time for the oil in the pipes and cat to burn off fully so dont get suprised if it doesnt all disappear at once - just keep a check on your oil level to make sure you are not using any more!
1999 156 1.8TS Sport Pack 3
2001 166 3.0 V6 24V Super
2003 156 GTA 3.2 V6 24V
2005 156 1.9 JTDM-Jet Sport
2008 159 1.9 JTDM Lusso
1997 GTV 2.0TS Lusso
2001 147 1.6TS Lusso