Yes, indeed, blank slate! Kind of fun, in the sense that when it is done, it will be uniquely your garden, an expression of yourselves. But the first thing you need is a whole bunch of patience. Realize that landscaping a big space like that (unless you have multiple thousands of dollars to pay a team of landscapers to design it and bring in a bunch of mature plants, in which case it is no longer your garden), is a project of several to many years.
So yes, start with putting everything in lawn, just so it isn't ugly and you can live with it while you do the rest.
Then make yourself a plan of your yard and start drawing out what you might want where. At this point, that would not be what specific tree goes where, but where you might want trees and shrubbery, where you want paths, a water feature (personally I think every yard should have one), kids play area, veggie garden, flower beds, maybe a gazebo / sitting area, fire pit, fruit trees, compost area, tool shed, etc.
That little patio out the back, looks like it just bakes in the sun. I would put an arbor or something over at least part of it for shade.
Since your house faces north, I would think about making a significant foundation planting -- not just that little patch in front of one window, but large areas on both sides, with some trees and shrubs that will get big. Your house is very big, you want something in scale, not just a row of little plants. And then I would put some kind of big hedge or row of evergreen trees out by the street, to break the cold north wind. People these days usually have their private space in the back yard, but your front yard would be easier to enclose. You might want to have a little fountain and seating area in the front with that shade tree Ramona mentioned.
Be sure all those north windows are very well insulated or your house will be cold. It is odd how they gave you all those north windows and hardly any windows facing the morning sun. You have that big blank wall on the east side. I would want a tree that will get big in front of that, but not too close to the house.
Things to think about ... think about planting with native plants, shrubs, trees.
Is a searchable database of native plants. Put in wisconsin and your conditions (full sun, how wet), what you are looking for like trees, shrubs, etc (do one search at a time) and it will give you a whole list, with links to info about each. Google WI native plants nursery and find sources for native plants. Native plants are adapted to your conditions, so once established, they will be very rugged and hardy and low maintenance. And they provide food sources for birds, bees, butterflies and other native insects and wildlife, that are adapted to use them and can't use the exotic ornamentals. Read Noah's Garden
and Planting Noah's Garden
by Sara Stein.
Learn to think about the habitat value of what you plant. Why plant something that just looks pretty, when you can plant something that also looks pretty, but has berries that people and/or birds can eat, that attracts beneficial insects, that feeds wildlife.
Do enough research, before you start spending lots of money on stuff. And keep asking questions here.
Have fun. Take lots of pictures of your project as it goes along! Keep us updated!