First do all the work that will involve tromping/tearing up the yard before you do the landscaping. Seems obvious, but it's not always followed.

To me the needs of the house trump the yard so did start there. I’m a unicorn that designs both, bunnies broad strokes in the yard the same way I do the kitchen. I may specify the deck locations, beds etc, but let the landscape pros select the plants and make other suggestions. The same way I design the kitchen but the cabinet designer will tweak my plans to fit on knife drawers etc.

The window can impact the front landscaping design. The decking will affect the rear. Get those planned before you involve a landscape architect. The landscaping plan can proceed before work on those other two starts because your landscaper can reserve plant material as soon as it becomes available with area nurseries for later pickup. Otherwise stuff sells and quality choices go first.

A good landscape architect can help with the backyard regrading and the front yard, but not with the window. You want any outside construction on the house done before you hire the landscape architect. You can certainly discuss the job with potential hires and see what they have to say.