The Parameter Object is very well documented for each parameter in each drive, so I go to the User Manual each time I use a Parameter Read. Most parameters are integers, but some are 32-bit and some are 16-bit. The internal units of the parameters are often not the same as the plain-language or display units.
An example from the 1336 Plus II drive user manual:
https://literature.rockwellautomation.com/idc/groups/literature/documents/um/1336f-um002_-en-p.pdf
The Output Power in kilowatts is Parameter 23. While the drive displays the power in kilowatts, the "Drive Units" that you would read via a MSG instruction are described as "4096 = 100% Drive Rated KW".
So if you read that value from a 22 kw drive that was running at half power, you would get a value like (11/22 * 4096 = ) 2048.
You'll need to check through the scaling and units for each of the parameters you want to read.
In general the I/O connection always includes the Command Word and the Reference Word in the Output side, and the Status Word and the Feedback Word on the Input side, so you don't need to read the drive status or the feedback.
I used to know all this stuff by heart, but it's been a while since I work on a 1336 Plus or Plus II. The Reference and Feedback values are 0 to 32767 for the Min Frequency to the Max Frequency.
In the PowerFlex drives, there are a lot more parameters that are in engineering units (like 0.1 Hz or 0.1 RPM) than in internally-scaled drive units. It's always worth it to check the user manual.