Sounds like you've made a decision not to cover any of the brick. Just to answer your question - the masonry adhesive is applied to the brick surface (not the Gyprock) in blobs approx 450mm apart. It sets pretty hard so to remove it at a later time you'd probably have to chisel it off. Any residue left in the surface of the brick could be touched up with brick coloured paint. Apparently you can also use cornice adhesive. Same way of removing & hydrochloric acid would remove any residue.

Rebecca - try oiling the timber and see if this brings it up. Rub it in with some steel wool and it can do wonders to bring life into the timber again and it is quite quick to do. The worry with painting is once that is done, you can't go back. I'm assuming you live in an area of similar homes so for selling purposes, I would check out all homes currently on the market in your immediate area, go to open house days, see how they have been renovated and gauge potential buyer's response to them, ask questions as to just what they are looking for in a home. Agents will help you with this too. I spent a year doing this before I sold my home and learned a lot from it. There are just as many people out there who want to put their own stamp on a home as there are those with no vision who just want everything pretty. Your front door, while it doesn't allow much light, could well be a significant heritage piece for the home so a solar tube or 2 could be the answer to bringing light into the space. Colourful artwork on the walls will then help detract from all the panelling too. Good luck with it all.

We recently updated an apartment to sell and got great feedback from the buyers on the paint - Dulux 1/4 Lexicon low sheen on walls and Vivid White high gloss on doors, picture rails and trims.

I agree with both your painter and your Google result. The issue is something that has soaked into the surface of the old wall, particularly as you had an odd result when cleaning. You can’t expect the painter to sand and paint as part of the original job but they may be able to offer advice and action if you’re prepared to pay them. If you want to DIY I’d be sanding the wall and trying some stain locker undercoat.