Hi there,
I can't speak specifically to your procedure, though I had a different version done last May. I had adult aquired flat foot secondary to posterior tibial tendon insufficiency and had the PTT repaired and an Evans osteotomy (insert a bone wedge on the outside of the foot). I was in a splint, then a cast, for 6 weeks (non-weigthbearing) and then a walking boot for 4 wks. I'm not sure what the timeline is for the arthrodesis...but there are others on this board who have had it done and will fill you in, I'm sure. I live in an apt building with stairs, like you.
I wasn't home for almost a week after surgery, as I stayed with family for awhile. I would say to take it slow in using crutches and have someone with you/behind you if you feel unsteady. If it's too much, you can sit down and inch up them...I did a lot of that too! You become pretty innovative...I walked on my knees, used my arms to "swing" down the stairs (walls/rail on both sides)...felt like a monkey!
The knee scooter is one great invention! I used one and got lots of looks and questions...felt like I should have been paid to use it, given the free advertising the equipment store got from me! It helped me be more independent for sure. I still used the crutches for instances where there were stairs or tight spaces. My arms became fairly strong after hauling all 20 lbs of scooter up and down the stairs each day, often more than once per day, and putting it in/taking it out of the car. It was worth it though!
I would recommend having a shower chair, a handheld shower head, a cast cover (ask your clinic if they have them), a basket for anything you might need (like the TV remote, cordless phone, pain meds, etc.). Get the handicap tag ahead of time if possible...it helps, even if you're not driving. Have some ice packs ready. Stock up on snacky type things and foods that are easy to make or heat up. Start working on your arm muscles...they're going to be used more than you know!
Hope some of this helps! Good luck on your surgery! This is a great place to learn more and post as you're recovering with questions/concerns or for support.