What are some things two people must agree on to keep a relationship?

[The Robster]

I'm 21 and have not been in a relationship before. By the end of this year, I plan to do so. Problem is, my mother seriously suggests that I get with "my own kind" (that being, gypsy women that work from home over the computer, probably do not have plans for college and probably have no GED/high school diploma). They also speak this obscure gypsy language that no one ever taught me when I grew up. Basically I'm just this white American dude.

Also, I'm the only agnostic in my family and they pretty much know, they just don't care.

The issue here is I don't know how different I'm "allowed" to be. What would be some of the things that we absolutely positively must agree on?
Take note this could be any couple ever.