Your revised plan sounds good to me.
Be careful using copper-based meds with plecos though, you may find that they are very sensitive to the meds and can become ill because of the copper. If I remember correctly, plecos are scaleless fish and as such very touchy about chemicals, especially copper. You may want to move them to a different tank for the duration of the treatment. They will be fine to return to the tank following the treatment, but the full strength of the med can harm them.