I had an Astrotrac in the beginning. But it took not lang and I wanted to have something bigger :-D
For the beginning, I think you won't need a guide scope. A guide scope needs a guiding camera and the guiding camera needs a notebook.
I would just start unsing the Star Tracker with around 100 mm focal length. When you are able to make a good polar alignment and you still get round stars at 3 minutes, then try a bigger focal length. When you are at 300 mm and want to have more than 1 to 1.5 or 2 minutes exposure time, then a guiding scope is necessary. :-)