What did you decide??

I have a separate guest toilet without windows using a ceiling extractor fan - not a problem. I also have internal cavity sliding doors to bathrooms and toilets and love how they give extra space and options regarding placement of items. Another location alternative for you may be between the cinema room and the kitchen, depending on what you had planned for that extra space in the kitchen. Two metres is a wide hallway, if that is what it is? Ours is 1.3 which is considered wide (as we need to accommodate a wheelchair which has to turn into doorways). An advantage of a very wide hallway is it gives room for extra furniture placement such as bookshelves, linen or other cupboards if needed. I don't see a linen cupboard or pantry cupboard in your plans. Something else to think about is future proofing - try to cover future possibilities with regard to function, as making structural or fittings changes later can be more expensive, and may come at a time when you can least afford it (e.g. injured, disabled, children, aging or other such people visiting your home). Lives change, sometimes over time, sometimes in an instant, and suddenly the doors are not wide enough (especially the toilet door!), or the walls are not strong enough for a weight-bearing rail, and a host of other things. We put 900cm doors as a minimum and it makes life a lot easier, including moving furniture in and out. Universal Design principles are worth a look. Sadly these considerations are currently considered special or optional, although there are moves to change that, so that builders and architects will consider these things as standard.

try searching for retro baths online rather than art deco, sometimes people don't really know its art deco. I tried a gumtree search, you could also post on some facebook buyswap sell pages and see, but I find people on gumtree are less interested in a side hustle and it can be cheaper. Its also easier to search.I found one listed in Cheltenham but there were a few others in victoria that were under $100 which might make a courier affordable.

Read the bottle of the cleaning product. It will tell you whether it is suitable for septic systems.