Being inexperienced with this site, I'm on my 3rd effort to reply back to you (of course I didn't bother to save a copy of my last two reply efforts, so maybe I'm getting more practiced at describing things).
I made a simple drawing of the routing result I'm aiming for, below another drawing I'd made a while ago. The older drawing's a rough picture of the end product, which will essentially be almost a quarter-round, where the sides and underneath connecting pieces are 3/4" ply and the "top" is 1/4" x 2" stock maple slats.
The edges of the slats need to sit into the notches I'd ~been~ thinking of effecting with a rabbet bit, but the other sides of the plywood pieces needs to be rounded essentially the way I'll be getting full un-notched edges treated with the bullet bit.
The simple drawing shows a side of the plywood with an edge partly rounded with bullet bit and 3/8" from top of ply (on other side from bullet rounding), there'll be the notch I'd been thinking of effecting via rabbet bit.
Thanks loads for any further thoughts you have. I'm fine with sticking to my two-part (bullet then rabbet bit) way of doing this unless that will more likely make a mess.
I'm all for learning,m but I also think I'd do well to lessen my appetite for buying more bits!