If the rumpus is going to be used as a family day care room, then I think the powder room should be accessible from there. This will make it so much easier for one person to supervise the kids in the room as well as the one who is heading off to the toilet. Perhaps you also need a wet area in there for cleaing up after messy activities. I know someone with a similar family day care set up, and they have toilet and laundry attached to the back of the garage/daycare space. And then the kitchen is adjacent, this makes life a lot easier for the sole person in charge of the kids.

Look at the range of timber bench tops at Bunnings. Nothing better than a timber look, with real timber. https://www.bunnings.com.au/our-range/kitchen/benchtops/timber

you need to confirm all the dimensions as there's some discrepancies in the sizes shown in your plan but my suggestions include losing the linen cupboard in favour of a bigger bathroom with space for full size bath, shower, vanity and toilet with linen storage in the vanity under the handbasin and toiletries in wide wall cabinets over the sink and toilet...there's a sliding glass door off the kitchen to an enlarged deck and a galley kitchen with old laundry becoming a combination laundry and pantry with wide counter for under bench washer and blind corner pantry and space for the fridge and removing only portion of the wall allows for an opening between kitchen and living with space leftover for stove, counter, drawers and wall cabinets and more counter with double sink, DW and drawers on the other side

Depends on how tall the users are. But if it is a 300mm cabinet, there should not be an issue. A standard 700 to 750mm should be okay. Taking into account how big the washing machine lid is, so is can open fully.