It is like car choosing and ownership, it's a highly personal thing with no fast set rules but one certainty is that when you do jump be sure to keep your mind and body running well and stress free.
Helping others less fortunate helps to achieve both if done in a discrete manner.
Working out how much you will need to maintain your expected lifestyle is simple maths but of course you need a big contingency fund for the unknown future returns

- that might just be me erring on the side of caution wanting to protect my good lady should I pop off before her.