dev, should you have a limit hash in order to avoid big hand or rental mining?
As someone said in previous pages that it is impossible to implement.
The point is that it is really difficult to rent high hash for NIST5

Minerals had it implemented (by keeping source closed during PoW and providing a centralized pool; some people were suspicious but it worked) so it is possible. Maybe not the best way but if the developers can be trusted it will work.
Yes, but by this way you are taking the risk of mining in a pool of the same devs of the coin. So the coin won't be plural and fair.
And also, somebody can cheat, and use several users/password to avoid the hashing block.