Hi, Chris,
I'm Judy, a Revit specialist, and I'll be glad to help out with some ideas. I see that you'd like to have a default height for your wall openings; there isn't a way to set a default height, but you might find it helpful to draw a reference plane in your elevations or sections as a means of aligning the tops of your openings as you draw them.
Another idea is to create the first opening of a particular size and copy and paste it as needed. If you click the Constrain box on the toolbar, the copies will be exactly aligned horizontally as you place copies left or right of the original.
It sounds like you are not the only user who would like to be able to specify a default height for wall openings, so I'd suggest posting the idea on the Revit Idea Station, or voting for the idea if someone has already posted it. This is a great way to let the developers know what functionality or features you'd like to see in Revit.
Let me know if this helps!
If this answers your question, please click the Accept as Solution button so others can easily find the answer.
Cheers,
Judy Staicer