You need one booster for each district.
Most boosters can be used be any command station, but check before buying.
Typically, the command station goes direct to boosters, not track.
Easiest way to do this is to feed the command station to a terminal strip with spade lugs. Then each booster connects to that terminal strip. For that small a layout, 18 Gauge should be fine as bus wire to booster.
NO connection between districts that does not go through 2 boosters. Completely separate wiring, including bus wires.
So, Power Cab to booster #1, to district 1, Cab to booster #2 to district 2.