1. yes
2. I will make a mechanic to save the game in safe rooms
3. not sure, there will be all kinds of puzzles.
4. since every costume has their own attributes, they should all look a bit different from eachother. but maybe some of your ideas might come close to what I will make. it's hard to say at this point of development.
5. save rooms might be spread like bonfires in darksouls : p because it creates fear
6. maybe there will be 1 occasion where a door breaks by an enemy : ) but it's not planned at a specific place yet.
7. not sure, but at least 2 variations of 1 type. (like 2 pistols, 2 shotguns, etc)