Looks like a cool addition to your arsenal, Rusty! Thanks for the short course, too.
I used to use the Cokin system on my last film camera (Minolta x700) for many years (1983 to 2006)...... Polarising, Red, Orange, Yellow (for b&w film), but never bothered with the slightly silly offerings (starburst, prism etc).
When I got my first DSLR the first accessory I got was a Cokin system again..... an adapter ring for each lens, filter holder, a set of Graduated NDs ("ND Grads") and a couple of straight NDs. They're good value and it's not a big deal to break one (which I have several times). The only additional expense incurred is with the NDs (you really need two or three of them for different strengths), and the ND Grads, where you may need three different densities and three different degrees of graduation, soft, medium, hard - i.e. the hardness of the transition from dark to clear - so you could end up with nine ND Grad filters. In practice, though, I make do with just two - medium density and medium 'hardness'. I use a wide-angle lens a lot and the ND Grad is nearly always on.
I also use Polarising filters - you can get them for the Cokin system but I prefer the quality of traditional glass filters for that.