Making attribute fields mandatory and sub-domains on both ArcGIS and AGOL.

I have several questions regarding attribute field properties on both ArcGIS 10.1 Basic & ArcGIS Online:

First, is there a way to make an attribute field mandatory to fill on a table in a geodatabase?

Second, is there a way to create sub-domains that cover one attribute that relates to the domain of another attribute field?

Third, if these are possible, can they be replicated onto the AGOL platform as well?

I appreciate any feedback on this topic.