Tell us about yourself!
As someone that has been a professional woodworker for the last 40 years I am offering some sound advise as to how a wood shop would handle this build. The time to route the top piece and the waste of material would NOT be an acceptable method for doing this build -- time and material equals money -- and in business we are not in the habit of losing either. Again having said that everyone here is welcome to do it your way and I'll do it mine. It's a nice instructable other than that.
Why wouldn't you just glue two small pieces of wood to the top on track instead of wasting the time and material routing out, gluing up, and then cutting off the bigger piece you used?
That is absolutely not true. You can precisely measure and cut two thin strips of hard wood and glue them to the base -- I like the instructable but disagree with the wasted effort and material to glue the top part -- so make it any way you want and I'll make it my way.
some minor modifications to make spinning it more easily / less effort. But then again compromise on portability and weight.
A larger flywheel would make it easier to spinning with less effort -- just slower on the start up.