The first problem is that high speed communication is mostly cut off from the surface, which means the environment is semi-isolated. Electromagnetic wave will get absorbed quickly, and sonic comes with several seconds of delay. Light / electric cable would require constant care not to mention if the later leak as salt water is very conductive. The second is the massive pressure in mid of the ocean, which the material is as expansive as say those used in space programs. 100 atmosphere is no joke, and that's just 1 kilometer (less due to higher density) below the surface. All the creatures there can easily resist the pressure which means our standard weaponry is useless not to mention their huge sizes compared to their fresh water or shore counterpart. And the predators can penetrate that kind of shell or even skin, which means it can as easily chew through our vehicles. Then there is geological factor, the temperature, the makeup, and not to mention the constant rusting with which be worsen if we try to zap the fish as that is the only viable option I can think of besides torpidos. The third is food source, as creatures are hard to kill or even fend off. We need teams dedicated to food production/ hunting and we need to set up power supply from the surface or develop some alternative source. (being really close to deeper layers does have perks, for example huge amount of thermal) The fourth is the ocean might already be occupied. Though even someone insane like me is skeptical about the possibilities.