How much I have to pay to the members who will promote it in their signature
It is your right to decide how much you want to pay, you can see the overview of all signature campaign here :
Overview Signature Campaign You may see the rate of other campaign and you can decide the rate of yours based on the average rate. Make your rate equal to other casino's campaign would be good.
how much I will have to pay to the person who will administer those participants.
You can make a deal with managers by asking them how much their rate for their job.
Can I myself start the signature campaign or only these managers are allowed to start the campaign for me?
Yes you can manage your own campaign without hiring campaign managers, be sure that you use an escrow to hold the funds for the campaign. But I would suggest you to hire one of available campaign managers on this forum for better campaign.