Screen reader support and browsers

Apologies if this has been asked before, but would appreciate any guidance.
Work is being undertaken to make our website more accessible, and we have the following questions...

1. What screen readers should we be looking to support and what versions of each?

Proposed:
JAWS is the optimised reader
NVDA as a supported reader
Windows-Eyes as a supported reader


2. What browsers to support and versions of each?

Proposed:
IE 11 - optimised
IE 8 - supported
Chrome - supported
Firefox - supported
Safari 8.0.3 -  optimised


Thanks in advance !
Erin
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