Three questions I have after reading Steem whitepaper

I have read a few posts about Steem and Steemit, the introduction posts which show the high-level design with nice metaphors. Since I'm looking to dive into the technology those readings were not really what I was looking for, so I upvoted them all (because they did a good job at giving an idea of what's what) and then moved to read the official documentation.

Reading the white-paper was very educational, it describes the economics of the system. It left me with three main questions that I will post down-here and please help me make my mind on them. I'm very curious to see what's under the hood of this community!

What is the adoption of Steem Dollars? In the white-paper they are described as a form of debt financing, if you buy them they will pay interest rate (~10% yearly, right?), to me this looks of very little relevance: if I want 10% per year I can enter an hedge fund which will have a way lower risk for the same return. Why should I want to buy Steem Dollars?

What is the longest confirmation time you have experienced while transferring steem? Steem doesn't have transaction fees, but a bandwidth limitation to protect itself from spam requests. It would be very interesting for me to see a correlation between Steem Power and confirmation time, in my understanding the higher SP the higher the bandwidth available for transfers, but it is not clear if also the transacted amount impacts the bandwidth. What happens if two accounts with plenty of SP start to send steem back and forth betweem themselves?

I honestly couldn't make sense of the mining process, but the best way to understand it is for me to setup a node and see what is it doing. If you like though please explain why we should not be worried of the following:
"The mining algorithm adopted by Steem requires the miner to have access to the private key of the account that will receive the rewards." If the machine is compromised, the miner loses all, that's quite risky, no?