Four to six classes a year, out of about twelve in total? That doesn't sound too bad to me. I took about that many non-major classes when I was in school, although they didn't build on each other like the curriculum I proposed.

I studied at two state universities. At both of them, classes were measured in "credit hours" corresponding to an hour of lecture per week. A regular class was three credit hours and semester loads at both universities were capped at eighteen credits, corresponding to six regular classes per semester and twelve regular classes per year (excluding summers). Few students took this maximal load, however. The minimum semester load for full-time students was twelve credit hours and sample degree plans tended to assume semester loads of fifteen credit hours, both of which were far more typical.