For ongoing support it might be useful to contact the Royal Blind Society or equivalent in your country. Someone there may remember / still use linux as their
operating system, and be able to help you, I know now they may be using JAWS which is a commercial Windows program. Ask for computer section or adaptive technology section. I believe they used to use lynx - a text based web browser to access internet. This may save you a lot of time trying to reinvent the wheel. Similarly try to find someone in your country that works for organisations that help people with cerebral palsy.
Your main concern regarding security is rootkits. Don't be led into a false sense of security regarding linux. Although a properly setup linux box is way ahead of windows, you still have to know how to set one up.
This endeavour is too complex, time consuming to try doing it alone, especially if you are new to linux, so please seek help from 'partners in crime'.