"Disabled" really doesn't tell us much. Are you visually impaired? Are you paralyzed? Do you have a learning disablity? Without knowing what your limitations and strengths are, no one could make any sensible suggestions. The more information you can give, the better the answers you'll get.
Best of luck.
yes to all you can get all these things but sounds like you will need a face to face to find out what would help you the most or even over the phone apple can help you with this by going to one of there stores or phoning them up.
Cover W/ Wireless Keyboard&Mouse?
Covers - Yes
Wireless Keyboards - Yes(Bluetooth models)
Mouse - No support in iOS for mouse use
Yes many third party styli available
Way2Optimize Siri Use?
Learned through use
Built in accessibility features that can be configured and include
High Contrast/Reverse colours
Hearing Aid loop connection
LED flash alerts (Uses LED Camera flash)
Assistive touch -adds wide area control blob if you have motor control deficiencies.