A thought: It might help to have an architect look over your plans before you start the renovations.
Not being an architect, and, after disclosing to you that I hate dormers on houses:
I vote for knocking out the walls on the first floor, turning that into your master bedroom and putting the bonus room on the first floor if you have the build-able yard space to do it.
The reason I would do that is because as we get older, our bodies betray us and sometimes stairs become an obstacle.
If you do expand upward, please think about raising the roof so that the walls of the room or rooms you have upstairs will be at least 8' high. That increases the useful square footage of the space dramatically. Also think about putting at least a 1/2 bath in the bonus room so you won't have to run up and down the stairs whenever nature calls.
Think about putting radiant heat in the floor of the room you decide to use for sewing, even if it's just where you park your sewing machine. If I was building my house, I would also put it in our master bedroom, but that ship has sailed...
If your reno has a basement and that is where the washer and dryer are, I'd also suggest finding a way to move them to the main floor. It's amazing how much easier laundry seems when you don't have to run up and down stairs.
If you do wind up knocking out walls on the mail level, make sure you include the new wiring, outlets, phone and internet connections while renovating. You'll have the walls open, anyway.
Good luck, and have fun doing the renovation.