IMHO, the weight of the bicycle isn’t as much of an obstacle to carrying it up a flight of stairs, as the overall size of the thing. A bicycle is skinny, yes, but it is longer and taller than you realize, and has things that stick out, lol the pedals, handlebars and saddle. They can be very awkward to get through a (narrow) staircase, as found in a typical residential dwelling without bumping into the walls.
How heavy and awkward depends on your personal level of fitness, balance and coordination.

I won’t give you any recommendations on a specific bike to buy, because there’s just too many, but I will give you some general advice:

Go to a bike shop. There is so much information on the internet, that it’s easy to lose the forest for the trees; a shop will have a specific inventory , much easier to tell one bike from the next, when you can actually look at them. The shop staff should be able to, if they’re any good, be able to explain the differences between models and narrow down options that would fit your specific needs.

You’ve budgeted a pretty significant amount of money for this bike, but I’d recommend spending maybe a third to half of that. $700-$900 will get you a pretty capable recreational/commuter bike. As bikes get more expensive, they often get more specific in their capabilities, so you may be better served by a more basic model for your first bike.
A bike In that price range should last you for many years, as well. Bicycle components are actually fairly standardized, too, so finding common consumables like tires and brake pads is no issue. I have a couple of bikes over 20 years old, and one that’s almost 50, none of them require anything I can’t find within a few minutes of searching.

As to Folding bikes, it may be a good fit, considering your living situation, and as a city bike, they do pretty well. I also find that they’re actually pretty good for beginners and I’ve used them to teach new riders who have balance and motor control issues, as the compact frames and small wheels are easier to manage than a full size bike, especially at lower speed.
I don’t know that I would attempt a 20-30 mile sporting ride on one, but 2 or 3 miles down to the shops, is almost exactly what they’re designed for.