Your payoff from the job would be non-taxable provided it was not part of your contracted entitlements e.g. pay in lieu of notice.
On the shares the relevant tax would be CGT unless they involved exercising options
If they were selling shares you alraedy had the gain would be calculated based on the purchase price of the shares. There is an excellent post from Brendan on this site as to how this is calculated.
You are allowed 1,270 gain in any year tax free.
The gain is taxed at 25%
You state the payment is made in stages. If you have already done the deal to sell the shares, the Revenue position is that full CGT is due up-front, whether or not payment is deferred.
However, it is possible to claim a hardship provision to allow tax payment on receipt of instalments.
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