Sasidhar,
calling a COM component from BizTalk is just the same as calling it from any .NET assembly. That is you need to generate a wrapper, called a run-time callable wrapper or RCW. Search MSDN or Google for more details. Then you can just use the normal expression shape in the orchestration to call out. Of course you'll need to create a variable of the type in your C++ component in the orchestration variables.
To log messages just turn on message tracing. Or of course you can log directly to the event log from an expression shape.
For 3, I think you already had my reply in another list.
John D.