This doesn't have any logic:
1. I invested 100 dollars.
2. OK price is x2 and I pulled out my initial investment of 100 dollars.
3. Extra profit in time when price is rising, but what if price is going down? But let's say price go 3 time higher.
4. Prices for tropical country for whole family is minimum 2000 dollars.
5. To activate my 500 dollars crisis fund, I'm best case that much?!
6. Where we can go with 500 dollars.
7. Come back from holiday and you are in big dept.
8. To repeat what when I returned all the money?

Your strategy will work if you invest thousands of dollars, and who can afford to lose that much? Your strategy doesn't work much if you invested in wrong time! Read about people who bought at 19000 dollars, where are they now, and where is their profit?
Your strategy will work just if circumstances are perfect.
Don't fool yourself that this will work, I don't know what other people comment.