RIGHTTIREFIRE- first welcome to the forum. Great bunch of folks ready to offer help, support, and occasionally criticize your work. I have a similar path back into model trains but mine went from HO to O. I had a huge layout as a kid, two actually, that went into boxes when I got married and moved. I always kept a loop of track under the tree each year since. Fast forward to a few years ago when I finally convinced my better half to let me carve out a small corner of our small basement to build a layout. It's 4X8 but it satisfies my train bug and let's me keep the trains running year round. I have since bought way too much stuff (finally slowing down) and having a blast with one of the best hobbies around.
My point is that you may be able to do the same. Don't let the space constraints keep you from enjoying the hobby. Lots of great track plans for small spaces available. Don't be locked into ovals either. Shelf layouts along the wall can be fun too. If reversing loops can be fit then switching and running can be accomplished in relatively tight quarters.
I like what you are doing with the double loop for under the tree. My one suggestion would be to mount the track to either plywood or rigid foam board. It will help keep the track straight and also up off the carpet. Gives you an opportunity to do a little scenery around the tracks too. You don't have to use full sheets, just cut pieces wide enough to hold the track and make it in sections that can be easily assembled and then stored for the rest of the year.
Good luck and keep us posted on your progress.