I suggest you ring the Feast Watson support line and ask them and let them know what type of wood it is, eg solid or veneer and what type. I had such a difficult time deciding what to use on my wood benchtops in the kitchen, the product I used is perfect. I consider aftercare a big factor and the product support person helped me decide because of the ease of maintenance re accidental scratches etc.

first consider any good use of the space from inside the bathroom (you could then fill in the opening from this side for more walls space and/or shallow bookshelves etc and access storage from the bathroom otherwise add some adjustable shelves and a hinged door between the post and the wall and fill in the rest of the space and/or cut panels of painted craftwood that can be screwed over the opening and removed for access ... quicker and cheaper would be a curtain gathered top and bottom to conceal the opening and hide all your stuff

Can you add some pictures. Lot of balconies are accessed via bedrooms. Not odd really but I'm not a fan of it either. Most balconies off bedrooms don't get used much.

if possible swop the entry and garage stairs to walk up to a view through the gallery and away from the master entry... enclosing underneath the second level stairs and extending the wine store wall adds extra space to the pantry, wine store and mud room and some extra space counter next to the fridge for wall shelves or storage for display or glasses and counter for serving wine ...the side of the up-stairs could have open railing with underneath enclosed to allow alternate arrangement for the powder and ante room with an extra door to separate the laundry and powder room from the dining area (with extra soundproofing insulation around the toilet)