An all wire cage is a difficult home for a finch. No privacy from prying eyes. Having the sides and back blocked out with timber rather than wire will solve the problem.
Having the water vessel/feeding area blocked off with a privacy screen, be it a sheet, a towel or something else, will help the birds to feel like they have somewhere to be at piece.
Having the nest boxes setup with privacy from all sides will help substancially with breeding attempts/interest and overall results. You may have had success and that is great, however with a few more tweaks you will increase your overall results.
Just my opinion, although opinions are worth their weight in gold if they make sense to you.
