New Room Long wall or short wall?

Short wall. My first dedicated room was 10x15 and getting the distance behind the speakers seemed crucial. I did not have to toe my speakers in as radically as suggested above but experimentation with toe in is an easy tweak.
Most definitely treat the room. If you live in the Midwest, I recommend ATS Acoustics for absorption panels. Fairly priced and very quick delivery, even with special orders. No affiliation, just a satisfied customer.
Also, I don't think the Totems will be too much for the room. I was using a pair of Meadowlark Shearwater hot rods in my room and they worked very well.

FWIW, something else occurred to me about the long wall setup (which I've been enjoying many years now). There is known to be an audible comb-filtering effect from the rear wall the closer you sit to it. What I believe is generally not often taken into account here is that this can be mitigated at least somewhat by throwing the right amount and type of acoustic treatment on the rear wall. It's just that you don't often come accross users who've done this, mostly, I suspect, due to the WAF (as in my case). But, just whether or not such a thing could tip the balance for you in favor of the long wall, in practice I can't actually say. But, currently with my own rig with the seat along the rear wall and leaning forward in the chair, the presentation is at it's most 3D-like. When leaning back the presentation becomes noticeably more panoramic. It isn't as though it becomes flat. The difference is more like the difference between sitting in the first few rows vs the middle rows at a classical concert. In either case the system soundstage depth seems to extend well enough beyond the front wall and whichever perspective I prefer is at my choosing. I suppose I should add, however, of course, that true nearfield listening IME tends to minimize many of the soundstaging/reflection disadvantages of small rooms whether along the long or short wall.

Early on in the hobby I read somewhere that having speakers along the long wall is supposed to be the better setup for improved low bass when compared to the short wall setup. Fact or fiction?

In my experience in my room, bass enhancement was the only positive attribute of placing speakers along the long wall. You had to tame it, but it was there. In all other respects too numerous to mention, the short wall was better for me.

The Totem Forest sound best when they are placed 4 to 5 feet out from the back wall and ideally 2 to 3 feet from the sidewalls so it would seem that the short wall is your best choice. Unfortunately in this hobby there are no easy outs you must try it both ways to be sure. Happy Listening.