It won't take over unless you don't manage it for like 3 months. For good algae nutrient exportation, you should trim your macroalgae every few weeks so that it stays healthy (free of detritus and dark spots or yellow light spots) and this will export the nitrates and phosphates the macroalgae has absorbed from your tank.
If you put it in a darker location like a hang on back filter, it will need a localized light. I have a clip on led spot light for one of my tanks. Another option is to put it in a breeder insert inside the main tank, where it will stay contained and still get the main tank light.
If you chose to utilize the hang on back filter, i would recommend you alternate your lighting with a timer, so the light for the chaeto runs at night. This will actually help balance your tanks pH levels which can drop at night otherwise.