Military Upkeep Cost? Please Help!

[Omanes Alexandrapolites]

I didn't realize that different units had different upkeep costs. Is their a list or is it specified in the units information page?

It's specified in the unit's information page right at the bottom of the statistics column. It varies drastically between units, so should be taken heed of when deciding what to train.

I am not sure by what you mean by protectorate? I assume you mean if other countries are paying tribute?

The protectorate agreement is a kind of treaty that can be proposed by a diplomat to his enemies. You can read more details on how protectorates work here.