A lot of questions here, I don’t want to create a huge text wall.
TLDR: don’t sell or spend Bitcoin, use it as loan collateral
Taxes: easiest advice, don’t sell your Bitcoin. Small purchases are OK, and peer to peer, NOBODY reports these, up to a few thousand I feel perfectly safe doing that and not reporting any capital gains (which are gains only in a collapsing currency, not real gains.)
Major purchases (using Bitcoin): buying a vehicle or a house - hard to get away with unless you don’t file taxes - so for most of us, do what Robert Kiyosaki does: don’t sell, just take out a loan. Use the BTC as collateral for a loan to buy house, car, whatever, or even buy more BTC (Michael Saylor). He is issuing corporate bonds at 5% interest, and using the money to buy BTC that has a CAGR of 65%.
Using BTC to take out loans is similar to the Yen Carry Trade. People borrow ¥ in the Trillions at 0% interest, buy US debt at 5% interest, and collect 5% yield on money that cost them literally nothing. This is also known as a speculative attack. It continually devalues the Yen and supports the dollar. To stop it the BoJ could raise interest rates, but this would destroy their stock market and bond market and banking system. They are trapped and eventually the Yen will collapse. In this decade we will see 200 or 300 yen/dollar.
The USD can be attacked in the same way. Borrow dollars at 5% interest, buy BTC. Bank lending creates more dollars (they aren’t “loaned” from deposits, they are simply created), further devaluing the dollar and making the loan even cheaper to pay off in BTC terms. If enough large companies and rich people do this, it collapses the fiat currency while BTC goes parabolic. In 4 years, Saylor has taken his unknown software company from obscurity to being in the S&P 500 using this very strategy. Others will do the same.