If you use standard Vivarium wood it is dense and resists breaking down in water so no need to waterproof it.

I appreciate the technical build you are undertaking, but the questions you are asking make me concerned you are biting off more than you are ready to handle. A tank doesn't need to have all the bells and whistles to be an outstanding tank. That is a trap most people fall into early on. Lord knows I fell into it hard. Water features rarely work as you intend and end up being a LOT of work to get right even for those of us who have been building for years. Everyone when setting out to build their 2nd or 3rd or 4th or .... tank needs to stop and ask.. Why am I adding a river... Because I want it or the frogs. We humans tend to try to one up ourselves and our peers and that just what vivarium building is really all about.

I am more than happy to answer question as you progress through this, but I dont feel right being a wiki for you to embark on something you dont seem to be ready for

Paul