Yes bitcoin will remain dominant until the hard cap is reached.

What are the measures to keep your private key safe and in memory ? Are there any alternatives to retrieve the key back ?

I read somewhere of an idea to Create an ICO of an ERC20 token on Ethereum called Bitcoin, with 21M supply, is it actually possible ?

Germany recently approved bitcoin, why exactly is the approval required and what will happen after approval ?

You can assume the number of users in bitcointalk.org, its not accurate but you get to have the number to assume.

More than people in my opinion its the events that is responsible for the change in the bitcoin price manipulation.

It protects you against : Fraud, Identity theft, Higher middleman fee, limited access and most importantly you own the bitcoin.

A private blockchain is like an intranet, only accessible to those who have been granted permission to use it. So if you define success as enabling multiple parties to transact with each other – creating operational efficiencies for transactions that couldn’t otherwise be achieved through databases – then, yes, a blockchain can succeed without bitcoin.