slm9s, yes it's hard to give specific advice on what kind of bike people need or want. I will say this as far as BBSHD installs go, you don't have to worry that much about the weight of the bike like our pedal-only applications. That SX Trail is an awesome candidate for emtb. You mention "flowy singletrack", and in a pedal-only application this bike would be overkill. However, don't worry about that with a BBSHD. Also the 26" wheel deal won't be an issue either, I don't care what the 29'er only crowd screams...LOL! That actually is more of a feature on a pedal-only bike, but a 26'er doesn't suffer as much when you mid-drive one. I have a BBSHD in an '08 SC Nomad which is a bit in the same category as the SX Trail, and it has been an absolute hoot on aggressive trail and even just plain dirt road riding.
Back to your project, your frame does have "official" ISCG tabs. I know geosped here on the forum has trimmed his tabs on a big hit MTB to work with a BBSHD. He had more of an issue with the less common, wider, BB shell size. Your pic there appears to be the more standard 68-73mm size, so you should have no issue once you address any issue with the tabs. If your chainstays will clear a Luna Eclipse 42T chainring, you should achieve an optimum chainline. It was perfect on my Nomad. This is the lowest gear chainring you can install on a BBSHD, and it still allows my Nomad to achieve 40.8 mph in the 11T rear cog. If you've mountain biked before, you will find the torque of the BBSHD allows much less shifting and not require all the incremental rear cogs of the 11 and 12 rear cogsets. I'm running an 11-50, 9-speed rear cogset, but I could have easily gone with the 11-46 cogset instead. There is amazing torque available in this motor, and unless you're trying to start out or climb in the really high rear cogs, you won't hurt this motor and controller. I bring this up because your rear cogset looks like it may be quite small...perhaps?
On the battery, this is an area of application and preference that can be all over the board. I use a 52V, 17.5AM setup in a backpack. Others want smaller battery packs on their frame somewhere. The problem with some full suspension frames is battery location on the frame. You'll have to assess what works for you. My battery will power my bike for a good, long ride without battery anxiety...LOL!https://endless-sphere.com/forums/download/file.php?mode=view&id=298495
Here's a pic of mine for some reference.