Well... Sequence Text is broken with regards to this. You would normally set the Speed to Custom and the Custom Speed could be keyframed, but Motion overwrites keyframing this parameter with its own "idea". Since this doesn't work, then using the Stop behavior doesn't help much (and when it does, it "jumps" at its end to make up the pause it creates... not exactly what you want for a "natural" type on effect).
The only way (currently) to make this work consistently and correctly, select your text object and go to the Layout inspector. There is a section called Type On. You can keyframe the End parameter to create a type on/pause for each line as you like. Don't worry too much about precision at this point, once you keyframe all your pauses, you can go into the keyframe editor and adjust the keyframe "stop" points to adjust your timing for each line as needed. How nice this looks will probably depend on the number of lines of text and the length of your project which you can also easily adjust by clicking the "clock" icon under the canvas to that it show 12:15 and click and drag up on the timecode clock to increase the length of your project - click back on the clock icon [showing 12:07] to go back to timeline timecode. Remember to reset the Play Range out point to the end of your (new) project time and you will probably need to reset out points for objects in your project (move the playhead to the end and select your objects and type 'O' to set a new out point).