I think you should be aware of a well known adage in cycling. “Strong, light, cheap: pick two.” Your circumstances will not relieve you from the general truth here. Your desire to enjoy all three is nothing the rest of us around here haven’t struggled with as well.

The types of riding and activities you’ve described, optimally, call for different types of bikes. And while I think it’s possible to buy one bike that could do them all, it’s not possible that one bike could do all the things equally well. You’ll have to decide which riding style is most important to you and focus on finding a bike that at least favors that style.

Carrying a bike up two flights of stairs is a serious consideration, and pretty much dictates that “light” be the priority. You’ll have to figure out how much “strong” you can afford, because when strong and light come together it’s never cheap.