Gouache, just as any other medium, can be used in different ways as the artist works differently and has different experiences with it. Some of these artists are: Erik Tiemens, Nathan Fowkes, Thomas Paquette and Marc Hansen. These have websites and blogs that you might find helpful or inspiring.
It has unique properties unlike other watercolor paint. It dries quickly both on the palette and the painting. And the colors dry to a different value than when they were originally applied. In general lights appear lighter and darks dry darker. It dries in a matte, suede-like finish
It generally works best on a rigid surface. This is a good area to explore and experiment as there are many new surfaces now being offered by manufacturers. Each of these will have different results and texture when finished. The entire painting can then be finished with varnish.
Using varnish is a matter for exploration as to the texture and result. It will allow you to place the work in a frame with a glass pane. Krylon Matte Finish spray appears to work well and provide protection without a glossy finish.
Some artists appear to love this way of completing the painting and others range from simply not preferring it to completely opposing it. You can experiment with some smaller works to see what works best for your style.
An artist who is doing quite a bit of experimentation with gesso is New Mexico artist, Deborah Secor. She is most known for her pastels but has explored with small sizes of gouache paintings. Her website is: ://www.deborahsecor-gouache.blogspot.com