The PoS difficulty can be found in several places.
1) In the header info/status of the block explorer.
2) With your local wallet, mouse-over the green check-mark in the bottom right--it will display PoW & PoS difficulties.
3) Within the wallet console, you can run several commands that will reveal info such as network difficulty. Type "help" for the command list and info.
4) There may also be a CLI parameter you can pass to the wallet to get this info, but of this I am less sure of this off the top of my head...

Inputs are the "containers" that hold "x" coins. A single address can have many inputs "within" it.
Please refer to the concept of inputs/outputs/addresses as it relates to blockchain--good info to brush up on.
The wallet evaluates each input as a separate "batch" of coins with a corresponding age.

Age for TZC PoS is explained in the whitepaper and in various supporting docs on the website, etc.
If you read up and still have questions, please feel free to come back and ask for clarification.

So generally speaking you are correct.
The # of coins you have (organized by input) is multiplied by the coin age.
This produces your coin weight.
Coin weight is loosely the PoS equivalent of hashrate in PoW mining.

That should hopefully get you started and pointed in the right direction--good luck!