1) If DRK goes to, say, 10 bucks a coin in the mid-term, we are talking about 10.000 usd for running a node. It could be too much.
Maybe this can be adjusted as the value the 1,000 DRK represents changes?
2) 10% of the mining for last node sounds too much. It also may open up a window of exploitation and give incentive to DDOS in master nodes so that one node takes the fee instead of the other... Other types of exploitation for getting the mining reward could spring up as we go along.
10% of the reward is not much if you will get it only once in every 1000 blocks. Dunno where the sweet spot is though.
There will be too many nodes running for anyone to dos them all.