what is the absolute minimum of software installed inside cFP-2000?
I use LV 8.5.1, the last allowed version for cFP-2000.
Are there other limitations in older Versions? LV6.1, 7.1?
What are the purposes of the parts?
as you stated correctly LV 8.5.1 is the last version that supports the cFP-2000 system.
There aren't any limitations regarding FieldPoint with older LabVIEW versions in general, but not all FieldPoint driver versions are supported by older LV-versions, so the restrictions mainly result from the driver you're using.
The minimum installation for FieldPoint is:
The FP driver is needed to recognize and configure the device, the driver also includes the programming API. As the cFP-controller runs an Real-Time Operating system you will need the LV real time module to be able to program it.
Hope that answers your questions.
Watchdog is not mandatory, you can run succesfully your applications without installing it on cFP. Actually, I don't know the steps to configure cFP in newer LV version, but in MAX based configuration, you can simply uncheck Watchdog software in installation page.
About LV Realtime module, you need it to program cFP, i.e. to develop your own application and run it in cFP, so it is required.
Hope it helps!