OP, if you decide to follow that article make sure you copy chainstate folder first and perform work on that copy. If you're not being careful, you might corrupt the chainstate which force to perform reindex which take hours.
Yes, you can extract information about the total number of wallets and historical data related to the number of addresses with a non-zero balance from Bitcoin Core. Bitcoin Core provides a full-node implementation of the Bitcoin protocol, and you can use its built-in commands to access and extract various statistics and data.
Wrong, Bitcoin Core doesn't have address index and snapshot feature which is necessary for OP works. That means OP need different software to generate the stats or write one by himself.
You can using pywallet for do it.
pywallet is software to restore wallet, not obtaining stats from blockchain stored by Bitcoin Core.