Manage iOS Developer Enterprise Programs for several companies

I am a sole trader and I have developed an iPad app that I'm going to sell to several companies independently. They are small companies (<50 employees) that have nothing to do with IT and it would be a nightmare for them to register with the Developer Enterprise Program. That's why I'm probably going to register for each of them. 1- Can I register for several Enterprise Programs with my Apple ID, or does it have to be done by someone inside the companies (with a different ID each time that then adds me as as admin)? 2- In that case, am I going to be able to register on their behalf (if they provide me with their apple id + password? or if I appoint myself as the contact for Apple?) 3- Do I even need that program to deploy less than 100 apps to iPads?