Yes, the physical verisons will be DRM free.
At the moment the only operating system that is supported will be Windows.
The physical edition is all-ages. It can be upgraded through Backerkit to a complete 18+ version. More information can be found here: http://solpress.co/projects/sakurasakura/faq/
You can view the dakimakura upgrades here: http://solpress.co/projects/sakurasakura/faq/
You can see what the addons look like here: http://solpress.co/projects/sakurasakura/faq/
The original mosaics will be included with the game. 18+ scenes will be removed for the all-ages version.
The patch will be released immediately with the game. It will be provided at no additional cost.
The Collector's Edition will come with the physical game, physical soundtrack, and the physical artbook, in a Collector's Edition box.
Don't see the answer to your question? Ask the project creator directly.