really good questions 1 - the fact that transactions do not require identity make btc intrinsically "private" but the fact that transactions are completely public and wallets can be discovered with analysis is not so private. add in corporate exchanges that require irl identities and you have something that's only a little more private than a bank account unless you take precautions like mixing coins.
2 - they don't mold, they gather in chunks, this can increase your fees if you have lots of small chunks, kind of like the burden of dealing with small change.
3 - yes every transaction since that 1st pizza is "the" blockchain. no real danger of loss since nearly every wallet on earth has a complete copy of it.