Thanks for posting! Congrats on the new place and lots of space! While a room this long and open might seem intimidating now, it’s really exciting to have lots of area to play around in while designing!
It sounds like you already have a direction with your sectional and chaise plan, and I would recommend thinking about all of the furniture you’re going to end up putting in this room. A living room isn’t just seating, but usually also entertainment and some decorative storage like bookshelves. If you’re having a TV in your room, plan the layout of the furniture so that you have a logical viewing area. Likewise, if you are putting up bookshelves or any other large structures like those, you’ll know to make create a nice reading area in front of that, or maybe to leave the shelves alone! Another general rule is to put the longest piece of furniture (which in your case will probably be the sectional), along the longest wall.
Otherwise, I recommend getting a rug or two to tie the space in together, and to use smaller accents like wall art and floor lamps to fill in some of the bigger spaces.