The model is called a
'Kit', because you sort of assemble it from the tube, ends, and reflectors. (Simple to do). It's their most inexpensive one, and the same sized tube and tray as the 'Go'. The Go is more portable in some ways because it's got the reflectors built into a zipper case so it's quick to set up/take down an throw it in a bag, but the reflectors are smaller so I chose the Kit and am glad I did. I don't throw it in a bag, and figured if I wanted to travel with it I could make a zipper thing and use those larger reflectors. I also have their 'Fusion' which is much larger, so that'd be better if you want to have sliced sandwich bread. It would be round slices though, lol.
Regarding how I use the last dough with the next batch: I don't do anything scientific with it, I just don't use quite all the dough from the last batch and then plop it in with the new batch when it's mixed before mixing them together. I also don't wash out the container I kept the last batch in before adding the new for the fridge. This is only when I want it to be sourdough, of course.
Sometimes I've kept a sourdough batch and a non-sourdough batch so I can use either according to my mood for the day I use it. Generally though, I don't have it every day, and fridge space is limited, so I like to just start anew each time and let it gradually get sour as I use it. That way it changes and I've had both kinds over the course of it. For your purposes, since you want to go sour all the way, you'd want to skip starting anew after the first time. I'd monitor how it's going after several batches though, as I haven't gone more than about 4 or 5 times without starting anew, so don't know how it'd be after that.