1. I don't know about the pre 1995 rules, but incapacity benefit has been taxable for a long time. Contributory ESA is also taxable.
2. There are two categories of ESA - work related activity group, or support group. You should have been told which of these two groups you have been placed in. If the letter you have does not explain this you need to query it. If you are in the work related activity group your contributory ESA (which is not means tested) will stop after 12 months & you will have to claim income related ESA (which is means tested) if you are entitled to it. If you are in the support group your contributory ESA continues indefinitely.
3. If you have been placed in the work related activity group & think you should be in the support group you need to appeal. Go to your local CAB for help with this.
4. So far as I am aware, incapacity benefit has not been given an end date, but the pre 1995 rules may have been different. ESA can have an end date in some circumstances - I think these relate to the support group but am not certain.
5. Can you clarify your point about mobility - I don't see its relevance. Are you referring to disability living allowance? If so, that is quite separate & has its own rules.