I think you first need to look at your general area and the size and style of homes there. Attend open homes and check what others have done or not done and the price they sell for. Even look at returns on leasing according to the style and condition of the house - Estate Agents will happily help you with this. Depending on movement in the market around you, this can take time, so be patient it will be worth it in the long run. You can be a little adventurous with any upgrades when people are upgrading and renovating all the time, just don't to too far with what you do or how you do it to avoid overcapitalising or limiting your market. I'm also finding a lot of buyers are resisting ultra modern homes, they like modern but not too OTT so beware of adding features that may not appeal to everyone. Again, studying the type of people in your area will give you clues as to the type of people who will want to buy into the area, the type of lifestyle they have and what they want in a home. The trend to putting ceramic tiles in kitchens and casual living areas is fading and they are much more expensive to take out and replace. Definitely not a good idea if you decide to lease as they can be broken or even pit if not cared for properly. I'm presently looking to buy a new home and I'm seeing too many homes where tiles have been destroyed which is going to be a very expensive exercise to replace. If you are going to lease, keep things simple. I think Oklouise has nailed a very simple plan although I would take the toilet from the laundry, some space from both the kitchen and living area and put a separate powder room beside the laundry so you can make it more attractive for guests. One slide-in door from the hall opening to a lobby with the laundry going off one side and the power room the other, would take care of any odours or noise. The washing machine and dryer will make noise too. I don't think I would attempt to create a master suite downstairs, I know many who agree with me on this, but dividing bedrooms over two levels tends to create "fractured" families. You certainly won't want to be running up and down stairs all night to a restless or sick toddler. It then becomes too easy to have the toddler in your room and that can be a very hard habit to break. Three bedrooms are sufficient for many people so a simple upgrading of the bathroom, wardrobes (if necessary), flooring and window covers should be all that is necessary for the upstairs. The emphasis these days seems to be more in living space and entertaining especially when it includes generous outdoor areas , so I would make that your priority.

Good idea, Rachel, to have a master plan before doing any renovating. The last thing you want is to have to redo anything, especially given the costs involved. May I suggest you add a site plan, google view of the roof line, details about building structure and any restrictions you have, any views you have and a north/south indicator. Also helps to mention the area’s climate including prevailing wind direction. Are you a family? Two littlies and a dog, three roommates, grandma, son, older grandchild? Is the office for WFH, or would a study desk be enough? Do you need three toilets, or is the room between the kitchen and main bathroom actually a laundry? What currently works, what doesn’t? All this information will affect what is achievable, and how best to go about it. My first thought was to extend Bedroom 3 to create a Main Bathroom and study (or laundry and turn laundry into study) but no doubt the Houzz community will have many other ideas. But without the specifics, including a ballpark budget, they’re a bit constricted

your dimensions are not very easy to read so my plan has approximate measurements and my suggestions include a new master suite in the original house with a wiw and ensuite that can be used as temporary family bathroom during renovations and to keep the renovated back rooms for daytime activities with maximum north facing windows, low storage (under window seat?) for kids' stuff, an optional fireplace and wall space for TV (external electric shutters would screen western sun in late afternoons during hot weather) and avoid removing the old external wall supporting the original roof near the old toilet as i think that could risk more roof leaks and the extra floor space would be too cramped for a study nook without compromising space needed for the family room (the old toilet and storage could be used for more storage or maybe add that extra space to bed 3) ...there's a generous new mudroom, laundry and pantry and some changes to the existing kitchen but, change the central hinged doors to the back verandah for sliding glass doors and swop the other back door to a window to keep traffic centralised and away from floor space needed for kids to spread out without being underfoot .... final costs depends on too many variable but assume much more than you expect but imo it's not cost effective to consider clerestory windows in an existing roof so check out Solar Skylights for a quick improvement in daylight for any windowless room as they can be relocated as renovations progress and consult your builder about removing walls, changing plumbing and to help plan best locations for any windows that need to be changed for the new pantry and laundry and Roof Windows and/or ventilating skylights can be considered for the bathroom and dining area after you discover the impact of the new north facing windows in the new family room

I would have a long built in desk top on the window wall, this would give approx 1500mm per person. Then the computers would have their backs to the window, and the people can look out. Even if the window goes to the floor, you can still have a desk in front of it. Other two walls for storage, printer etc etc. ensure you have power points, internet connections above the desk for ease of use, and then enables underbench storage.