1. No, it is like the BTC/BCC change, you will have the equivalent assets duplicated to the new system. The new system works from the base, hidden underlying currency on Steem called VESTS and will be renamed to JUICE. The values will be identical from this underlying base from Steem. <br /><br />SBD is being removed because it is complicated and confusing, and may do bad things to the supply parameters. The conversion rate is frozen as at around midnight 5 August 2017.

2. The password is actually the secret key, the blockchain stores the public key. It's like a key and a lock. You hold the key, the database holds the lock, and if you have the key, you can unlock the lock.

3. Preminers are the people who were mining steem before it was publicly accessible. It was publicly accessible, but only to people with high level technical skills, and only advertised in a small, limited forum (bitcointalk). They basically generated about 8 billion Steem tokens, and they have been using this to manipulate the forum since anyone could sign up and post. <br /><br />It was thought by the Steemit Inc people that this would be a suitable way to fund development, but most notably, users like berniesanders/nextgencrypto/randowhale have used this power abusively, to manipulate people, and indeed, most of the preminers have abused users this way. It also has allowed them to basically fleece investors who have bought into the platform, they buy in, the price goes up, and the preminers then sold, price goes down.