if you want to be able to open the doors, load the boot and walk around i think you need at least 9m x 7m but if you to also want useable work benches and storage spaces (eg for the lawn mower etc) add at least 1 m to width and length

If you search DIY banquette on Pintrest you’ll see instructions and measurements. Most are in inches but you can convert them. Could you measure the seat height of the chairs you are using with the table (you need the table first) subtract the cushion height and that will give you the bench height. It does depend on the height and weight of those that will be using it the most, to get the best fit.

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

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