Short term no, long term yes. It's uncomfortable now because you're not used to it. As you develop the back muscles necessary for good posture, you'll feel better in the long run as it'll take pressure off your spine.

It's more comfy and it lets you breathe more easily, but you need the muscles for it. It's only a relaxed neutral position if the muscles at the back pull just as much as those at the front.

It is more comfortable, after you establish the discipline. Getting there takes some practice, which is probably why people slouch.

A good rule in my experience is to have the top edge of the monitor roughly level with your eyeline, so it's easy to see the entire display without needing to tilt your head back at all.