Hello fozzibear

I agree With Bryster Lights and textures will add a lot to the render time and file size but also the Amount of Boolean Objects you are using will add more to it as well and by the sounds of it you are doing quite complicated and big models. What I suggest you do is make them into different modules and save them as .obp and put them all together once your happy with the results. Also Skies and Clouds will also add a lot to the render time and file size. if you are using Lights have them on a lower setting the brighter they are the slower Bryce will be. Also here is a chart of the render options (basic only I am afraid for a more thorough guide go to youtube David Brinnen has a excellent tutorial on how to play with render options)

 

here is the link to youtube

http://www.youtube.com/watch?v=8WTYURTvXkw

and above is the file tutorial

 

Regards

Karl