I’d definitely use a solid door for the toilet. Do you actually need the sliding door into the living room? It’s not a very big house and I think the metal sliding door is too much. A method you could use, which fits with what you’ve done/have so far is to a more classic approach to the fixed elements of the house and then move to a more modern/transitional approach in furnishings. Mixing modern and traditional elements for the fabric of a house successfully is a skill that most amateurs don’t have.
I like the furniture and rug you have pictured. I’m not sure what size table you have planned but make sure the chairs fit.

Yes we definitely need a door and there are also quite wide architraves there as well so we'd need to remove it all if we don't have a door as I think it'd look weird and unfinished. My partner also really wants to keep a sliding door there.

The chair fits with the table. The image is just to show the design - the size will be a bit different.

Do you think these options are “lighter” or again not suitable?
https://idealbarndoors.com.au/images/stories/virtuemart/product/44.jpg
https://idealbarndoors.com.au/barn-doors/metal-glass-barn-doors/steel-glass-barn-door-bds03.html

I think painted wooden barn doors (like below) can give a more modern look but I have no idea which colour would suit or if this is right for the space. I think timber grain or white needs another timber accent in the room to tie in with which we don’t have.

I prefer a painted barn door to the black metal one you posted. Colour depends if want to make it a feature or blend in with the wall colour.
Can you post a pic of the current timber and glass door in the living room? Given you aren't keen on it, I'm wondering why you are going timber and glass doors in some of the other rooms? Is it the bulkhead that is more the issue?

Yes, brushed nickel on all the doors. You can see all the doors from the passage so they need to be the same.
I would go for a sliding barn door in the same profile as your new bedroom doors.

Why a glass door on the WC. When the light is on you will see the movements..of the occupants. Privacy?

You said there is a bulkhead on the sliding lounge door. Are you sure this is not a wooden pelmet that covers the door mechanism.

I would double measure the dining table with the chairs pulled out for sitting. Is there enough room?

That orange floor in the kitchen is all I can see....are you re staining that?

Yes pelmet is probably a more accurate description - sorry I wasn’t sure what that part is called! I don’t mind timber and glass as a combination but the door itself is old. The previous owner seems to have damaged the glass too so it needs to be replaced. Given that I’m replacing all of the doors, I thought I’d do that one too. You can see it below.

The floor is more ochre than orange. I wasn’t planning to do anything to it and not sure if that’s in the budget at the moment. The table and chairs will definitely fit. The table is available in different sizes but that’s the only image online.

Happy to consider other door styles if you have any suggestions

Love the kitchen cupboards, the door at the end of kitchen seems to have the handle set really high

Thanks for the pic - definitely a pelmet, not a bulkhead - it is why I asked for a pic to see what you had!
I would do the same profile as your other doors - either solid or with the glass depending on what you prefer. If you don't like the pelmet, perhaps think about changing to a hinged door, given you can't use the wall space anyway. Depends if space available for swinging of course.
You mentioned that you were concerned that the living room would look stark and super-modern with the black glass door. But you have traditional cornices and the wall colour (pinky beige from what I can tell from pic) is far from modern. Are you changing these elements?

Dreamer, thanks for your feedback on the floors. I’ve done a walk around and now I can’t unsee it! 😁 Looking into stain colours for the floorboards too now lol

Thanks Liz. I’m aiming for something in between modern and traditional, or I guess a combination of both. I’m keeping the cornices but the walls will be painted Dulux White Exchange Half, the ceiling/cornices Vivid White and the skirting boards, trim and doors in Snowy Mountains Quarter. I’m planning to do a feature wall in the hallway (the part of the wall directly behind the sliding door) in Missouri Mud.

Thoughts on this door (painted white) as an alternative to the metal door or do you think the timber barn doors would be better? I think I'd need to keep the pelmet with this style but not sure. Due to the furniture layout, it needs to be a sliding door.

Yes that style door would look good. it just depends how much light/privacy you need from the hallway into that lounge room, to whether you keep with a glass door, or go a solid door.

I like that style door. You can put the barn door style hardware on it. The track comes in black and chrome, even Bunnings has the fittings. No need to keep the pelmet to cover the tracks. Exposed tracks are the fashion.

I love these barn door styles a little different but would look beautiful

Thanks dreamer and bigreader. I’m not sure if that door is available in the size we need. I’ll check with the supplier.

Thanks for those photos Julie. Any suggestions for door colours? I guess I could forego the feature wall and paint the door that colour instead (Missouri Mud).

Our couches are light grey and the decor has green and brown accents (cushions, vase, ornaments etc). The bookcase and tv unit are white.

Looks like Bunnings has nickel finish tracks/hardware too: https://www.bunnings.com.au/rolltrak-barn-door-track-top-fix-set-satin-nickel-2000-x-40-x-6_p0011865

Hume doors and Colonial Warehouse stock doors in styles that will work with your existing choices if you need alternate suppliers.

Thanks, I found the right size at Colonial Warehouse

I don't think you need to worry too much about matching metals and I think black is incredibly versatile in that it can look both modern and classic. It's more things like sidelight profile which date doors. I'd try and go for glass in your sliding door as that already exists. 
Here is a glass cavity slider I have which I have either side of a double sided fireplace to close off a living space. So versatile. But probably more modern than look you are going for.

Looking at your picture I'd try and widen the opening the full "width" unless something behind the wall and go for glass French doors

I think barn doors look better in wider spaces.

Thanks CP. The current door is 2040 x 1020mm. We can’t go wider as there is built in shelving to the left which we’d like to keep. I’m looking through some barn door options too.

Any tips or suggestions for selecting a floor stain colour? I'm thinking something light.

I've got a quote from a company for custom doors similar to the below (one door, not two like the double door one). I think they look great but trying to visualise it in the space. Also looking at some vintage glass doors too. Will post pics soon.

Just came across this one too - can be made in our size with different glass options (not all shown)