2. Is there a good calculator for ROI and estimated rewards ( per day ) that calculates 5-10 years in the future or allows an input for estimated future value of BTC ?
No calculator will be able to calculate ROI of a cryptocurrency investment in terms of future USD value. For example, one can affect Bitcoin's price by banning bitcoin mining, by investing in Bitcoin (like Blackrock), by tweeting a things about Bitcoin by influential people, like Elon Musk did when he created a hype around BTC and then tweeted some bad staff about it.
Bitcoin can be 20K, 100K or 3K or any number in 5-10 years. No one can predict it.
3. Will BlackRock and the central bankers be able to fork BTC into a proof of stake coin? ( How are changes to BTC created ?)
Like said above, anyone can fork bitcoin. Blackrock can fork bitcoin, they can also create their own coin but in the end, it will be meaningless if no one other than them support it. Also, if BlackRock manages to acquire a lot of bitcoin, it will increase bitcoin's price and at the same time, if they fork and move on PoS Bitcoin, no one is stupid enough to follow Bitcoin that is led by BlackRock. Current OG Bitcoin is not popular without a reason.