I just have a plan if I want to join the delegate, what percentage of the profit do I get if I at least 100 coins are at stake
That would be about 0.02 ARK per day.
But 100 ARK are like 35, you wouldn't expect a real profit by investing just that, right?
I would advice you to invest at least 1000 ARK and hold the profit from staking, ARK will surely reach at least 5 again so with 1000 ARK you'll be making about 0.21 ARK / day and when the price reach 5 that will be about 1 / day.