I don't think that is brass but copper plate. These wheels are almost for sure cast pot metal (cheap zinc and other stuff) with copper plating to hold nickel or chrome top plating. Cast brass wheels would triple the cost of that loco.
I have three of these that I'm converting to battery RC. They are obviously very simple. They run well on track power even without sliding pickups. Keep in mind that the couplers are not at standard LGB height and the commercially available adapters interfere with the rear axle on the tender versions, so converting will take more work. I haven't run them enough to test durability, but at $50-$100, I don't expect much. (I spent about $70, including shipping.) Motors and gears look to be serviceable, but Bachmann has a habit of cheap coatings on the drivers. So, they are simple and usable, but I wouldn't recommend them as the basis for an otherwise expensive and time consuming kit bash. I plan to make them available for the grandchildren to run as an alternate to the omnipresent Thomas line.
I've been using a Bluetooth module made by Monocacy Trains. They have gone out of business, but fortunately the software is still installed on my phone. The unit is small, 17x67mm, but doesn't have a speaker. I use small, self-contained Bluetooth speakers set loosely in the cab. The phone app provides sound over the same Bluetooth connection that controls the engine. The Bluerail system is a variation that is still available. As time and funds permit, I will probably convert to the PIKO or the RailBoss 4 systems. I will have to defer to others for information on installing the Flysky as I am not familiar with that system. I have used MyLocoSound modules on some other engines and find them to work well and install easily.