BTW just to clarify
The 4 points above aren't a sequential list or in order of priority they are just examples of other strategies which I think avoid selling and hence wasting materials.
Building only 1 CB and selling excess materials, wastes materials.
You can't change the number of materials you get on trains etc. You might be able to change the split. But you can definitely manipulate (=optimise) how you use them so very few are sold or wasted.
They are not a sequential list and not either/ or. I use a combination of some / all of them at the same time depending as well on other priorities. It's also something of an iterative process too, working out the best fit
Although finishing the new zoo enclosures is low priority. I won't sell any materials needed for the zoo even if there is an imbalance. Simply juggle the other techniques to optimise what I have and don't have.
After all as you say, you've plenty of time to juggle and go thru iterations while you're waiting for materials to arrive. Townshp is designed to make you wait (or pay LOL ) Unless you pay Tcash you can't eliminate the waiting.
Best you can do is optimise what you have to minimise that waiting. Selling/ wasting materials just to reduce an imbalance will take more time in the long-run, and is very unlikely to be a best solution.