Whether it "needs" them or not, they are there - an inevitable result of a Universe dominated by gravity. Supermassive black holes may have an important role in star formation, but this is still an area of active research.
Black Holes.
Even though black holes suck through parts of the universe, the universe is inevitably big, and growing so as the universe is being sucked into another dimension by black holes, it is also expanding.
There are already black holes within the universe
Black Holes' can 'eat' any type of matter in the Universe.
Probably stellar mass black holes
The universe likely contains millions upon millions of black holes.
No.
The black holes may not devour everything since the outward velocity of the matter in the universe may escapethe gravitational pull of the black holes. Stephen Hawkins reckons that even the mass in the black holes would diminish over time, though over trillions and trillions of years.
Primordial black holes are theoretical black holes that could have formed in the early universe. They are thought to be small and have a wide range of masses. If they exist, they could have implications for dark matter, gravitational waves, and the evolution of the universe.
No.
Unlikely. The universe is a very big place, even next to the largest black holes we know. For a black hole to suck in the entire Universe, it would need to be nearly as massive as the universe itself. There is no way that such a black hole could form.
No, the universe is not inside a black hole. Black holes are regions of spacetime where gravity is so strong that nothing, not even light, can escape from them. The universe is much larger and contains many galaxies, stars, and planets, including black holes.