I am not sure if it is possible to buy Steem Dollars directly with BTC. You can only convert it from/to STEEM; or earn it via creating content. There seems to be a misinformation in the post. That is why, I summarized my MODEL in a reply above. Pasting my model below again and requesting you guys to cross-check it pls:

Steem:
Buy (with Bitcoin)
Convert with Steem Dollars
Power Down (from Steem Power, in 104 recurring months)
Transfer from another account

Steem Dollars:
Convert with Steem
Earn via creating Content on Steemit (%50)
Transfer from another account

Steem Power:
Buy (with Bitcoin)
Earn via creating content on Steemit (50%)
Earn via curating Content on Steemit
Earn via being a Witness (Mining) on Steemit Blockchain
Power Up (from Steem)