In the creation kit, is there a time limit on how long a speaking sequence can take? Or do you have to break it up into parts. If so how long is the max sequence?

I don't know if there is a limit or not, but from a user standpoint, if you are going to display the text on screen, it would be best to break it up into readable chunks, avoiding a wall of text that is difficult or daunting to read. If your voice acting is such that you want to showcase it, then smaller snippets are less likely to be clicked through.

Lines of dialogue are limited to 149 characters in length, including spaces. You can 'fake this' and try to get around it, but facial animations are generated based on the text here, along with some other important pieces. Long story short, you have to break everything up into 149 character lines and there's no getting around that.