12V LED radial wiring
You just described something like rail lighting system used in museum and such… they did it with halogen burners, but it applies to LED lamps too. They solved the power drop simply using bars as conductors and also hanging the lamps mechanically.
So it seems a fine thing if you are using an adequate wire cross section (adequate as in, depends on the distance). It is actually easy to predict the loss (it's just a resistor, you can find the wiring tables online)
One thing, however: some power supplies have a maximum length of cable supported on the output (for regulation reason, it's complex), just be sure to check it can handle your wiring. As for the group dimming/switching just do it in the obvious way, start with a 12V backbone/star/ring (depending on the placement) and then tap out the branches.