This is super cool some great ideas and work come out of hackathons!
How much should I request from the DHF for the prize pool?
A: Not sure what the normal rates on these are but I would say anywhere from $10k - $25k should be sufficient to get people involved and make some headlines since you want to go as public with it as possible and make it worth their time. Make it all Cash no gimmick prizes like ipads or whatever.
Should I create a proposal for marketing the hackathon?
A: Yes, this is what the pool is used for the betterment of Hive.
How many winners should be eligible for the prize pool?
A: I'd say 3 Even with a $10k budget you're looking at a sizeable pool for all 3 $5k $3k $2k
One phase or two phases?
A: Two depending on how many enter will kind of determine this as well. Two allows you to find promising ideas and push forward with them into the next round so perhaps the first round is a lower win value and the second is where the big win comes in to provide motivation.
Got any ideas to make the Hackathon better?
A: Off hand no I'm not sure how the last ran.
Would you be participating?
A: No - just the QA guy lol the one the devs hate ;)