Ferret, darters are supposed to have an erratic motion, that's why they're called darters
As far as the roll on the swimmers, are you making with long narrow bodies? It has been my experience that if the front of the plug is thick/wide relative to the tail there is less roll. Roll is not all bad, pikies have a roll to them but it is combined with a wobble, this seems to be appealing (to the fish). Maiking adjustments to the lip may help correct some of the excessive roll but this is how you learn. I had the roll lesson about a year ago
If you don't see it for yourself and you are just told about it, the lesson just isn't the same
As far as wood splitting, what kind of wood? Hardwood dowels (can't remember the type of wood typically used) split if they aren't sealed. White pine swells and cause your paint to crack if not sealed, basswood will also split. Cedars (eastern white, western red, alaskan yellow) are all good choices for (depending on the plug). Sounds to me like your day was very educational. Oh yeah, write everything down as it happens that way you don't repeat mistakes
Mrpogie is definately the guy to ask about bottles
One more thing I forgot, the way you weight a plug and the density of the wood you use can also contribute to roll. Hope this helps.