I'm new, as you know, so take with a grain of salt, as you will.....

1. The top 500 (random number, enter number there that you see fit) miners in the last 30 days or X blocks should be able to vote. Same people are the only ones able to submit ideas to be funded.
2. The percentage of income to the "treasury" would depend on the emission scheme of the coin, but assuming something like bitcoin, 1 percent of the block mining and 1 percent transaction fees should be enough. I think Dash's 10 percent is way too high.
3. No end time on the treasury, ongoing.
4. Unspent treasury is distributed to all miners equally (based on work over the 30 day period or whatever period). If no agreement on spending can be reached then automatically distributed in this fashion.