You 'need' as many as you can get. I understand it's attractive to set targets but the best strategy is to continually acquire and not focus too much on specific numbers.

However, if you like thought experiments, here's one. Let's say arbitrarily that approximately 4 million bitcoins have been irretrievably lost, and a projected world population of 9 billion people some time in the next 10-15 years, then there is on average 1,700,000 satoshis per person. I would suggest that people focus on getting their first 1,000,000 then beyond that simply keep on stacking.