please post the original floor plan and proposed upstairs showing dimensions of all rooms

yeah sorry I'm struggling to follow this plan.

I would consider including a shower in the proposed powder room, as taking out a bathroom reduces the value of a home.

the staircase space looks much too small but we need measurements of both upstairs and down to be able to consider the location properly..anything else would be a very expensive guess

There's a lot of duplicated posts appearing on Houzz lately, I wonder what;s causing that problem, Houzz hasn't picked up on that it appears

Thanks for you responses. First two pics are from designer, the third is a suggestion from our builder (also suggested by one of commenters) If we used the 'New Guest Room' space, we could eliminate the need to use the cloak room for wardrobe.

Not sure if that helps, but we are just trying to maximise small ground floor space as much as possible.

Original floor plan

Ok, I'd stay with designers plan. Add study in perhaps if its not costing much more.

Stairs are good spot to make both levels work.

I hope you've got a very detailed quote from your builder for this project because it definitely looks like a project where the Reno vs knockdown-rebuild cost comparison will be important as it's quite a detailed looking Reno.

It’s looking to be about $460K... we can’t get a 5bdr 2 1/2 knockdown rebuild for that. We are in a flood zone & all figures are $600-700K for a new house

My only comment is that the laundry looks to be in a strange location !

I can understand why the renovated bathroom is positioned there , BUT if it was my choice , I would probably swap the two , or even consider whether , just an example , its worth doing a smaller guest bed and have the 2 side by side , and add a Walk In Robe in the Master or similar . . . . . . .

Pottsy99 .... this was my thought exactly... but the staircase position?

the original staircase location feels much better but we can't be sure without all the dimensions missing from the sides of the plans... there's no separate lounge upstairs or down and you need to add furniture to test how the rooms work and why push out the rear wall such a small amount across the family room? there seems to be a lot of demolition and rearranging when it might be more cost effective to add a bigger extension at the back instead of knocking out so many internal walls but can't be sure without understanding the dimensions of the original house and block of land

I was assuming you would leave the staircase as the designer intended -- as soon as you move it , you have to redesign 2 floors , and with the outline you have given , I wouldn't even take a wild guess at that -- that would be a whole seperate exercise that needs way more personal info as well as construction materials , sunlight , blah , blah , blah .

The only comment about the stairs where they are though -- the 'guest bedroom' , if you leave it approx where it is , may be able to get a wardrobe or even small study/office ( with bi-fold doors ) under the stairs -- logical , but not shown that I can see .

I think there are a lot of compromises here that could be better thought out. The master is too small. It has less than half the robe space needed. The upstairs wet room has little space to dry yourself and hang towels and downstairs en-suite is also too small for size of house. Consider putting master upstairs where the study can be wir and en-suite, one guest bed and shared bath/powder downstairs and study. Or shared with laundry.
The garage door to porch should be at front of garage otherwise the extra storage space on the garage is wasted. I’m also not seeing enough linen cupboards for storage.
Try placing furniture, tv and storage on your plans taking note of windows and views.

Upstairs option

It looks like not much is being kept from the original home. So it's hard to tell really how much rearranging can be done. Also wondering about the side setbacks. Normally a NE spectacular would be much nicer than a NW aspect, which will get very hot on summer afternoons. so if it's possible it would be better to flip the garage location to the NW corner. The master can then have NE & SE windows.

If possible, orientation should really be considered in any new build or remodels of a home.

https://www.yourhome.gov.au/passive-design/orientation

my suggestion has much less demolition including keeping the original outside back wall in favour of a simple skillion roofed extension for kitchen and alfresco, this adds a similar floor area but the shape of the extra space is much more comfortable for dining and family rooms with kitchen servery and extra storage across the full length of the dining area..the new location of stairs keeps everyday traffic out of the living area to create a more private master zone with wiw and ens, group activities in family, dining, kitchen and alfresco plus easy access to laundry, guest bath and bedroom from everywhere and upstairs for generous kids zones..new location for internal access from the garage and more storage in the entry

Heaps better okl

I don't have time to draw a floor plan but wonder why something like the following wouldn't better. I see the entrance as becoming an unnecessary dog leg and waste of space, I would prefer opening up through from the new Porch to the new Alfresco