You're currently a very generous man ?
I have the following remarks and questions:
1) XLM Price is always going to be a roller coaster. If you're thinking to have this challenge periodically, it's better to fix the prizes in USD value.
For example: You can have first prize equal to 2000 USD paid in Lumens at the exchange price of distribution date. And same time, you have to put a maximum limit of prize in Lumens as XLM price might suddenly crash to epsilon then you will have to pay millions of Lumens ?
By fixing the prizes value, the challenge would always have fair reward for all winners.
2) I hope SDF will support this initiative and similar ones so challenge will continue. Their build challenge rewards is the best way.
3) When Stellar sign up program resumes, we should see more users in forums as many will come to ask questions.
And my questions are:
Who will decide the winners of this challenge? Is it the admin alone?
If 15th May comes and quality threads are not present, are you going to extend the dates of competition? I'm not sure if we have a 800 000 XLM thread at the moment but still 10 days left ?