Hello bryan-imhoff!
Thanks for your feedback.

There is no centralised database, all the voting, reward-distribution and staking mechanics are performed directly on the Steem blockchain using Steem-engine. Regarding cross-posting, there will be a specific tag for each post and if a user doesn't want to have the post show on Steemit, he can simply tick a box and it won't show on the Steemit interface.