keep in mind that my plan has single external walls and all the inside and outside walls are 10cm thick to make drawing easier and the depth of the verandahs includes the eaves, adding a brick veneer would use more space and given the choice it would be lovely to plan for a covered walkway and raked ceilings in the living areas and this is a very basic gable roof but there are lots of more exciting/expensive roof options to consider

2500 x 900 or the 1000. Aim for 1100 - 1200 between benches.

if you open the door in the middle back against the basin at one end and toilet at the other the minimum space to to consider would be about 90cm x 190cm and use the smallest toilet and basin depths but would be better to post the whole floor plan to see all the options

1.4 x 1.4 is pretty pokey , and no , I suspect an 820 door will be too wide unless you swing it outwards , which is just weird . If it swings inwards , even if it at 90 degrees to the toilet itself , there will be almost no room for a person , a WC and the door 'swing' . Most doors are at the end of the room , the WC at the other end , and that will make it even worse -- if the WC protrudes 50cm from the wall , and your door is 820 , you have 8cm in which to stand ! Setting the WC 'offcentre , the door off-centre the other way gives a bit more space , but add a basin and you have an obstacle course to negotiate . Is there any way you can take the length to around 1.8-2 metres ? A width of 1.2 works , 1.4 might sound better , but with only 1.4 of length you are pretty much stuffed . .