Posting a drawing of the floorplan would be helpful here. Do you need an office? what would you use the bonus room for, teen hangout?

Honestly we need a lot more info and a to scale floor plan. Also since it is a walkout what is beyond those doors?

Only you can answer that question. You need to decide what you want to use the space for first.

Dance Studio? Music Room? Movie Room? Office? Bedroom? Workout room? Pool table? Bar? Shuffleboard? Table tennis?

Only after you figure that out can you start looking at how to use your space.

I updated and added some more info

I have a large finished basement (similar in size to what you're talking about) which is divided into two rooms, home office and family room (large TV with two sofas). The TV area is at the bottom of the stairs and the office area has a 48" opening from the TV area that has solid core double doors (to keep the noise down). Without a floor plan I can't tell where you should divide the room, but I suggest you draw your floorplan on graph paper, cut out office furniture pieces and whatever you expect to put in the other room on the graph paper so you can move them around to get an idea of what layout would work. This is the old school way of doing it if you don't have fancy software. :-)