the vulnerability of traditionally gessoed ground to water media

First, I would not seal a panel intended for an animal glue bound ground with anything, including shellac. It is far preferable to size the panel with two coats of thin animal glue. The shellac will promote delamination.
Second, I hate to throw a monkey wrench into your plans, but high sheen water gilding can only be done on an animal glue bound ground, preferably with an animal glue bound bole layer. Any water-resistant coatings like acrylic dispersion paints may possibly prevent adhesion but will certainly make burnishing impossible. When one burnishes gold leaf in water gilding, they are actually burnishing the ground and animal glue bound bole and not the metal leaf. It is not even necessary to use a glue solution during gilding since there is such a surplus of glue in the bole and ground.
I am sure that if you use animal glue or fish glue to adhere gold to the surface, it will likely work, it just will not be burnishable. The result will be a matte.
I would not suggest applying MSA varnish below oil paint as this will increase the chance that the painting could be harmed during future cleanings.
Finally, if you go ahead with a procedure like you describe with its complicated, disparate materials mixtures and stratigraphy, please record your process on the back of the panel to aid future conservators in devising and appropriate treatment protocol.

More thoughts:
Since you will not be able to do burnished gilding given your plan, why use the animal glue ground at all? You could size a panel with an acrylic dispersion ground, apply a sandable, hard acrylic dispersion ground, paint in acrylic dispersion colors, then glue gold leaf to that layer. I am not sure about the most appropriate adhesive for this. I do not know if animal skin glue would be a good adhesive over the acrylic dispersion paint, it may bead, etc (test first). Certainly, most of the commercially available water borne dispersion/emulsion gold sizes tend to be too “rubbery” to scratch through and retain a sharp line. Perhaps one of the harder acrylic dispersion mediums would be appropriate. GAC 400 comes to mind but this is outside of my purview. I am just thinking (writing) out loud. I will send this to other moderators.

I agree that water gilding is probably not the best technique for your paintings. Water gilding cannot be applied as specifically in certain areas only. For detailed and more controlled applications oil gilding or acrylic sizes are more suitable, but cannot be burnishes. You can do a whole surface in water gilding and polish only certain areas, then apply MSA Varnish followed by High Flow Acrylics. It is not possible to paint with oil paints over MSA Varnish as the UV light stabilizers hinder the oil paint from curing, so the oil paints remain tacky (see  https://justpaint.org/?s=painting+with+oil+over).
Removing gold leave locally, as you suggested, is also not easy. It would require physical abrasion and most likely you would scratch into the paint layer underneath. If this aspect of applying and removing a gold layer is the most appealing to you, then you could consider using an iridescent gold color. The OPEN Acrylics would give you a few hours of working time before it sets up and iridescent oil paint dries extremely slow, but you can control that by adding a fast or slow drying alkyd medium.
The best thing for you to do would be to practice water gilding on a test panel and that will quickly give you a better understanding of the technical possibilities.
One more idea that comes to mind is, if you build up your layers with acrylics, as Brian suggested, you could create you first pictoral layers with the High Flow colors, then apply one or two coats of Isolation Coal, apply oil gilding on top of that and while the oil mordant is still relatively fresh, you can remove the gold leave with OMS and Q-tips or a rag. The Isolation Coat should protect the acrylic paint layer underneath during this process. Afterwards you can continue painting in oils. 

​I don’t have expertise in gilding, so I can’t address that area of your question.  I can comment on the importance of applying a layer of cloth to a support with a wood-grain surface (solid wood or plywood).  I’ve seen examples of paintings on wood and plywood, no cloth between the wood and gesso/paint layers, in which the grain pattern is telegrpahing through, cracking the gesso and paint. In once instance, this happened very quickly.  I consider it an essential step.

I consider it essential to adhere fabric over wood panels before adding gesso or a chalk-glue ground. What you propose may work, but as I stated above, please record all of this on the back of the panel. Any solvent-borne, non-oil containing varnish would cause the same concern (MSA, Shellac, Dammar, etc). Even with the acrylic dispersion layer, the MSA could be undercut using traditional, solvent methods.  The conservator may need to use more complicated cleaning methods. Perhaps the work would be left unvarnished.