Hello ilkeeper, Welcome to the forum
I use a single speed bike and I like it very much. But, I do have to admit the bikes I have built for others were multi-speed and I found it much easier to pedal with them then my single speed.
As far as changing the wheel and the horsepower of the titan....I am not sure. Hopefully someone else can jump in here and give info on that. And I will keep a close watch so that I will know for the future.