I used Simpson screws on my hangers. Screws have a better hold than nails and I find them easily to install.
yes any lumber that is used for floor joists inside and outside treated lumber
https://www.familyhandyman.com/decks/building-a-deck/how-to-install-joist-hangers/ has pictures and additional information
Tapcon screws would work fine. You can also attached a 2x4 to the wall then attach these hangers to that. It would make the job easier.
Simpson makes hangers for rough sawn wood which may work for you. They are bigger.
Yes depending on your application.
No predrilled is not necessary. However if you are close to an edge it is recommended to avoid splitting the boards
Yes, 100% recomended, just be sure to buy the right size. For example if your joists are 2X8, don't buy a 2X6
Yes, that is exactly the intended application
The 2.5" will make it into the header and should be fine